AMENDMENT NO. 2
TO
FORM S-1
REGISTRATION STATEMENT
UNDER
THE SECURITIES ACT OF 1933

1801 California Street, Suite 500
Denver, CO 80202
(888) 985-7363
(Address, including zip code, and telephone number, including area code, of Registrant's principal executive offices)

Sameer Dholakia
Chief Executive Officer
1801 California Street, Suite 500
Denver, CO 80202
(888) 985-7363
(Name, address, including zip code and telephone number, including area code, of agent for service)

Approximate date of commencement of proposed sale to the public:
As soon as practicable after the effective date of this registration statement.

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933 check the following box: o

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. o

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. o

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. o

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of "large accelerated filer," "accelerated filer," "smaller reporting company," and "emerging growth company" in Rule 12b-2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. o

The Registrant hereby amends this Registration Statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment that specifically states that this Registration Statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933, as amended, or until the Registration Statement shall become effective on such date as the Commission, acting pursuant to said Section 8(a), may determine.

The information in this prospectus is not complete and may be changed. We may not sell these securities until the registration statement filed with the Securities and Exchange Commission is effective. This prospectus is not an offer to sell these securities and we are not soliciting offers to buy these securities in any jurisdiction where the offer or sale is not permitted.

SendGrid, Inc. is offering 7,700,000 shares of its common stock. This is our initial public offering and no public market currently exists for our shares. We anticipate that the initial public offering price will be between $13.50 and $15.50 per share.

Our common stock has been approved for listing on the New York Stock Exchange under the symbol "SEND."

We are an "emerging growth company" as defined under the federal securities laws. Investing in our common stock involves risks. See "Risk Factors" beginning on page 15.

We have granted the underwriters the right to purchase up to an additional 1,155,000 shares of common stock to cover over-allotments.

The Securities and Exchange Commission and any state securities regulators have not approved or disapproved of these securities, or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Neither we nor the underwriters have authorized anyone to provide any information or to make any representations other than those contained in this prospectus or in any free writing prospectuses we have prepared. We take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. We are offering to sell, and seeking offers to buy, shares of our common stock only in jurisdictions where offers and sales are permitted. The information in this prospectus is accurate only as of the date of this prospectus, regardless of the time of delivery of this prospectus or any sale of shares of our common stock. Our business, financial condition, results of operations, and prospects may have changed since that date.

Until , 2017 (25 days after the commencement of this offering), all dealers that buy, sell, or trade shares of our common stock, whether or not participating in this offering, may be required to deliver a prospectus. This delivery requirement is in addition to the obligation of dealers to deliver a prospectus when acting as underwriters and with respect to their unsold allotments or subscriptions.

For investors outside the United States: Neither we nor the underwriters have done anything that would permit this offering or possession or distribution of this prospectus in any jurisdiction where action for that purpose is required, other than in the United States. Persons outside the United States who come into possession of this prospectus must inform themselves about, and observe any restrictions relating to, the offering of the shares of our common stock and the distribution of this prospectus outside of the United States.

PROSPECTUS SUMMARY

This summary highlights information contained in greater detail elsewhere in this prospectus. This summary is not complete and does not contain all of the information you should consider in making your investment decision. You should read the entire prospectus carefully before making an investment in our common stock. You should carefully consider, among other things, our consolidated financial statements and related notes and the sections titled "Risk Factors" and "Management's Discussion and Analysis of Financial Condition and Results of Operations" included elsewhere in this prospectus. Unless the content otherwise requires, the terms "SendGrid," "company," "our," "us," and "we" in this prospectus refer to SendGrid, Inc. and where appropriate our consolidated subsidiaries.

SENDGRID, INC.

Overview

We are a leading digital communication platform, enabling businesses to engage with their customers via email reliably, effectively and at scale. Our cloud-based platform allows for frictionless adoption and immediate value creation for businesses, providing their developers and marketers with the tools to seamlessly and effectively reach their customers using email. Since our inception we have processed more than one trillion emails.

Increasingly, today's transactions are digital. They happen online and are often automatic and recurring. Consumers want a seamless experience and have come to expect that their online activity will be recorded in their email inbox. Email serves as the system of record for a consumer's digital life, delivering purchase receipts, shipping notifications, account information, social media updates, reservations and website login data. Email is the primary communication channel in the digital world, with an estimated 125 billion commercial emails sent every day, according to a 2017 Radicati Group report. Email is also a trusted marketing tool for businesses. An email-based promotion can reach the right user at the right time, with a high degree of certainty that the user will see it. According to The Inbox Report 2017, in 2016 nearly 80% of Americans checked their email daily. According to a 2015 Direct Marketing Association report, email demonstrated the highest return on investment among all forms of digital communication, generating $38 in revenue for every $1 invested.

While email offers a compelling value proposition for businesses, effective email delivery at scale is complex and difficult. Inbox service providers, including Google Gmail, Microsoft Outlook and Yahoo! Mail, evaluate incoming email and block the delivery of harmful or unwanted email. However, these filters can also prevent the delivery of wanted email. According to a 2017 Return Path report, only 80% of wanted email reached its intended recipient. To manage email delivery on their own, businesses must understand the complexities associated with both sending millions or billions of transactional and marketing emails and the unique dynamics of numerous inbox service providers. Dedicated servers and databases, domain expertise, continuous monitoring of email protocols, and a team of people are all necessary to maintain a robust internally-developed email communications system. The use of developer resources in this effort can reduce businesses' investment in product innovation and other priorities. Without an effective, easy to use system, marketers seeking to reach customers via email can also expend significant time and resources without accomplishing their marketing goals.

SendGrid was founded by developers who were frustrated with their own experiences in managing email delivery. They wanted to build a system "that just worked" for developers and allowed them to focus on strategic business activities. They developed a robust technology platform incorporating their domain expertise and created an application programming interface, or API, that allowed for easy integration by businesses. We built our business model around serving the developer, including self-service adoption and a frictionless user experience. We have extended this platform over time to serve the similar email delivery needs of marketers.

We offer our customers three services: our Email API; Marketing Campaigns; and Expert Services. Our Email API service allows developers to use our API in their preferred development framework to leverage our platform to add email functionality to their applications within minutes. This service enables businesses to send thousands or billions of emails, all with the same high level of service and reliability, and incorporates proprietary technology and domain expertise to significantly improve deliverability rates. Our Marketing Campaigns service allows marketers to upload and manage customer contact lists, create and test email templates, and then execute and analyze multi-faceted email campaigns that engage customers and drive growth. Our Expert Services help businesses further optimize their email delivery. With our platform, businesses can achieve industry leading email deliverability that translates into higher brand engagement with their customers.

Our category leadership, self-service model and company culture have enabled us to attract and retain customers and employees, and continue to develop innovative solutions for email delivery. We deliver our services through a self-service cloud-based subscription model, where businesses primarily sign up for our services through our website. We offer transparent and affordable pricing, generally on a per month basis by volume of email and typically paid by credit card. In addition, we have robust documentation for onboarding and ongoing usage. This self-service delivery model has enabled us to rapidly attract customers while operating our business efficiently.

Businesses of all sizes and across industries depend on our digital communication platform. As of September 30, 2017, we had over 58,000 customers globally, an increase of 36% year over year. We believe a relatively small number of businesses have more than one unique paying account with us, and we count each of these accounts as a separate customer. While we serve large enterprises, we primarily serve small and midmarket businesses, or SMBs, that rely on email to power their businesses and are rapidly adopting cloud services. Our self-service model has allowed us to efficiently acquire SMB customers that historically have not been a focus for companies that depend on large enterprise sales forces. Our robust platform and the increasing breadth of our services allow us to scale with our customers as they grow.

We have achieved significant growth in recent periods. For 2014, 2015, 2016 and the nine months ended September 30, 2017:

•: our total revenue was $42.8 million, $58.5 million, $79.9 million, and $80.2 million, respectively;
•: our net loss was $13.0 million, $5.9 million, $3.9 million, and $4.7 million, respectively;
•: our adjusted net income (loss) was $(12.2) million, $(4.5) million, $(1.4) million, and $1.2 million, respectively;
•: our net cash flows from operating activities were $(9.6) million, $1.2 million, $9.7 million, and $10.1 million, respectively; and
•: our free cash flow was $(13.6) million, $(4.0) million, $(2.5) million, and $0.2 million, respectively.

See "Selected Consolidated Financial Data" for more information on our adjusted net income (loss) and free cash flow and a reconciliation to net income (loss) and net cash flows from operating activities, respectively.

Industry Trends

Email Is the Primary Commercial Communications Channel in the Digital World

Businesses increasingly interact with their customers through digital channels. Many emerging businesses are digital first. They primarily engage with customers through online and mobile channels. Customers of these businesses rarely interact with sales people, collect paper receipts, track orders over the phone or mail in their bills. These customers depend on automatic email notification of their transactions and rely on email as their system of record for their transactions.

Businesses engage with their customers through email because they can reach a wide audience and personalize interactions, while trusting emails will reach their target recipients. Businesses now analyze demographic information, buying behavior and preferences generated by the digital footprints of consumers in order to create unique digital experiences. These dynamics have created the opportunity for more frequent customer engagement through more personalized, targeted marketing.

Email Is Highly Effective at Driving Customer Engagement and Revenue

Email accounts are widespread and each is personal to its owner and consistent across time, making email a highly effective method of communication between businesses and consumers. Many individuals change their home address more frequently than their email address. Furthermore:

•: The number of email users worldwide will exceed 3.7 billion in 2017 (source: Radicati Group 2017 report).
•: The estimated average number of email accounts per email user in 2017 was 1.7 (source: Radicati Group 2017 report).
•: 67% of consumers between the ages of 13-50 believe that email is essential to their lives and 74% said email is their preferred communication method with companies (source: 2017 SendGrid commissioned report).

Marketers rely on email because it is effective at driving revenue.

•: The median return on investment for email marketing is nearly five times higher than the median return on investment for social media marketing (source: eMarketer 2016).
•: Email generates $38 in revenue for every $1 spent on email marketing (source: Direct Marketing Association 2015).

Effective Email Delivery Is Difficult

While email offers a compelling value proposition, businesses struggle to achieve effective email delivery due to a number of factors.

The Email Recipient's Side

Inbox service providers, including Google Gmail, Microsoft Outlook and Yahoo! Mail, use sophisticated filters to analyze incoming email and prevent the delivery of harmful or unwanted email, often blocking wanted email as well. The cost of delivery failure includes not only the infrastructure expense associated with processing the email, but more importantly, the lost revenue for a business from a new or existing customer.

The Email Sender's Side

Maintaining an email delivery system is complex. Domain expertise, dedicated resources and the need to satisfy complex technical requirements are all required to operate an effective email delivery system, particularly at scale.

To deliver email at scale, businesses need expertise and dedicated resources. The complexities of email delivery include building and maintaining a sender reputation and navigating that reputation across inbox service providers, spam houses, blacklist managers and industry watchdogs. Email delivery at scale also requires dedicated infrastructure and management of contact lists as well as an understanding of protocols to communicate with the recipient servers.

Businesses Are Adopting Cloud Services to Reduce Complexity and Focus on Core Functions

Technological innovation has enabled businesses to improve efficiency, but it has also lowered barriers to entry. Businesses of all sizes must adapt quickly to changing market needs in order to grow and compete. As a result, businesses are turning to cloud services to manage complex and costly parts of their IT infrastructure and operations. Cloud services can seamlessly provide many of the critical, but non-core, components for a business, allowing it to maximize the value of internal resources by focusing on its core differentiating competencies.

Frictionless, Self-Service Models Are Driving High Adoption of Cloud Services

The ease of cloud service delivery is driving a move from multi-million-dollar capital purchases of on-premises IT infrastructure to recurring lower-cost subscriptions for cloud services. This change has increased the influence of line of business owners, developers and marketers in technology purchasing decisions compared to a traditional CIO-led purchasing process. With cloud services, developers and marketers exert greater control over how they allocate their resources.

Businesses Need to Effectively and Efficiently Send Wanted Email at Scale

Email is critical to building and growing customer relationships but requires significant resources and expertise to manage the complex underlying infrastructure. The developers and marketers who are driving purchasing decisions of cloud services need a transactional and marketing email solution that possesses the following characteristics:

•: Reliability: continuous uptime to send secure emails at any time
•: Effectiveness: high delivery rates and high consumer engagement
•: Scalability: ability to send billions of emails across a range of customer use cases, with the same level of effectiveness
•: Ease of Adoption and Integration: self-service onboarding and integration
•: Affordability: lower, predictable cost versus an internal system and accessible to businesses of all sizes
•: Platform Extensibility: integrated transactional and marketing email capabilities
•: Services and Support: expert help to obtain desired outcomes and enhance email marketing capabilities

Our Market Opportunity

Businesses of all sizes and across industries use email to communicate with customers and can benefit from an easy to use, highly effective email service. While we have customers of various sizes, the majority of our customers today are SMBs that are digital first and rely on cloud services to operate their businesses.

We estimate our total addressable market for both transactional and marketing emails was $11 billion in 2016. See the sections titled "Market and Industry Data" and "Business—Our Market Opportunity."

Benefits of Our Solution

Key benefits of our solution include:

Platform Reliability

Businesses rely on our platform to power their customer email communications. We utilize a robust global infrastructure that includes multiple co-located data centers and public cloud resources to host our platform. In 2016, our platform was available for our customers to send email 99.995% of the time.

Proprietary Technology and Domain Expertise Enables Effective Email Delivery

We significantly improve email deliverability through embedded intellectual property in our platform and industry-leading domain expertise. Our platform is designed to operate at scale across multiple inbox service providers. In the first nine months of 2017, we estimate that we achieved a delivery rate of 94%, as compared to a general delivery rate for wanted email of 80% for the 12-month period ended June 30, 2017, as reported by Return Path in 2017. Our delivery rates for 2014, 2015 and 2016 were consistent with our delivery rate for the first nine months of 2017. We also offer Expert Services to help our customers achieve the best outcomes for their individual needs.

Ability to Scale With Customers As They Grow

Our communication platform provides the same high-quality service to a wide range of businesses, from startups to large enterprises that send significant email volumes. Our Email API service starts with entry-level pricing that supports up to 40,000 emails per month and scales up from there. Our largest customers send more than one billion emails per month.

Frictionless Adoption for Developers and Marketers

We make it easy for developers and marketers to adopt our platform using a self-service model. We provide a flexible API setup to easily add email functionality to their applications, as well as comprehensive documentation to help developers write code in their preferred development framework. We have a community of over 2.7 million active users that serves as a resource for questions about our platform. Once a business is using our API for transactional email delivery, it is simple for that business to also use our platform for promotional and personalized email marketing.

Affordable and Accessible to Businesses of All Sizes

We offer our Email API service as a monthly subscription, with pricing based on email volume. Businesses can tailor the use of our services for their individual needs, without the need to commit to expensive, multi-year contracts. Our cloud-based services generally provide significant cost savings compared to an internally-developed system and free up internal resources for other tasks.

Extensible Communications Platform

Our platform incorporates extensible technology that allows our customers to expand their use cases to improve their customer communications. Our customers benefit from having a single platform for transactional and marketing email, enabling them to manage their customer contact data in a single place, leverage universal design templates and testing systems, and ensure high email deliverability.

Competitive Strengths

Our competitive strengths include:

Easy to Adopt, Self-Service Model

Our Email API and Marketing Campaigns services are designed to be accessed from our website and immediately useable. By reducing the friction that typically accompanies the purchase of business software and eliminating the need for complicated and costly implementation and training, we believe we attract more customers to try, buy and derive value from our platform. Our self-service model has allowed us to grow our customer base while avoiding the expensive customer acquisition costs typical of high-touch enterprise sales models.

Market Leadership in Email Service with Strong Brand Association

We pioneered the market for a cloud-based email API service and continue to invest significant resources to extend our technology leadership and brand awareness in our industry. We believe that the SendGrid brand has become synonymous with email delivery and is recognized as the industry standard for scalability, reliability and deliverability.

Significant Domain Expertise Around Email

We have processed over one trillion emails since inception, including over 325 billion emails in the first nine months of 2017. We have longstanding relationships and integrations with all major inbox service providers and email industry organizations. These relationships provide us with real-time intelligence and performance feedback that enable us to optimize the deliverability of the emails that we send and anticipate changes in email handling policies.

Large, Growing and Happy Global Customer Base

As of September 30, 2017, we had over 58,000 customers globally. Our broad customer base provides us with insight into digital communication trends and activity and results in word-of-mouth recognition that drives traffic to our website.

Proven and Well-Regarded Leadership Team

Our senior leadership team has a strong record of success of starting and scaling technology companies, including publicly-traded software companies. We have received numerous external accolades related to our workplace culture, including a 4.8/5.0 rating on Glassdoor as of October 2017.

The SendGrid Culture Defines Who We Are and How We Engage with Customers

SendGrid's "4H" culture has allowed us to become a dynamic industry creator that attracts great people and consistently ranks as a top place to work. We strive to create an environment where people can have a career-defining experience and do their best work. Our culture is the sum of our values, traditions, beliefs, interactions, behaviors and attitudes, and it is through our culture that we recruit and retain top talent. Our culture is in our "4H's": "Happy," "Hungry," "Humble" and "Honest."

Our Growth Strategies

Key components of our growth strategy include:

Continue to Add Customers to Our Platform

We believe there is substantial opportunity to expand our customer base both in the United States and internationally as the ubiquity of email and the digital transformation of businesses continue to drive market adoption of our services.

Expand Platform Features and Functionality and Grow Our Marketing Campaigns Service

We intend to grow our Marketing Campaigns service by cross-selling into our existing Email API service customer base, acquiring new customers and adding new capabilities and features. Furthermore, while we do not currently provide services in other emerging communications channels, such as messaging/chat platforms, in-app messages, online ads, browser and push notifications, and SMS, we believe that the proliferation of these channels creates further potential growth opportunities over time for us to help our customers optimize their communications across those channels.

Expand our Strategic Partner Channel

We have built and plan to continue investing in channel relationships with our strategic partners in order to complement the reach of our own customer acquisition efforts.

Continue to Grow Internationally

We generated more than 36% of our revenue in each of the last three years from customers located in international geographies despite having limited international infrastructure and no product localization. We intend to add more physical infrastructure as well as localized platform content and support that will enhance our attractiveness to international customers.

Pursue Select Acquisitions to Augment Our Features and Functionality

We intend to continue pursuing acquisitions that we believe will be complementary. For example, we may pursue acquisitions that we believe will enhance our services, accelerate customer acquisition, introduce different distribution channels and add talent and expertise to our organization.

Selected Risks Affecting Our Business

Investing in our common stock involves risk. You should carefully consider all of the information in this prospectus prior to investing in our common stock. These risks are discussed more fully in the section titled "Risk Factors" beginning on page 14 immediately following this prospectus summary. These risks and uncertainties include, but are not limited to, the following:

•: Our recent growth may not be indicative of our future growth and, if we continue to grow, we may not be able to manage our growth effectively.
•: If we are unable to sustain our revenue growth rate, we may not achieve or maintain profitability in the future.
•: If we are unable to attract new customers, retain existing customers or increase sales both to new and existing customers, our business and results of operations will be affected adversely.
•: Our limited operating history in new and developing markets and our rapid growth make it difficult to evaluate our current business and future prospects.

•: If we are unable to increase adoption of our platform through our self-service model, our business, results of operations and financial condition may be adversely affected.
•: Our growth depends in part on the success of our strategic relationships with third parties to sell our services.
•: Our future success depends in part on our ability to continue to drive adoption of our platform and services by international customers, and our international operations and sales to customers with international operations expose us to risks inherent in international sales.
•: If we are not able to maintain and enhance our brand and maintain and increase market awareness of our company and services, then our business, results of operations and financial condition may be adversely affected.
•: The market in which we participate is highly competitive and, if we do not compete effectively, our operating results could be harmed.
•: If our security measures are breached or unauthorized access to our or our customers' private or proprietary data is otherwise obtained, our platform or services may be perceived as not being secure, our reputation may be severely harmed, customers may reduce the use of or stop using our platform or services, we may incur significant liabilities and we may lose the ability to offer our customers a credit card payment option.
•: Our customers' and other users' violation of our policies or other misuse of our platform to transmit offensive or illegal messages, spam, website links to harmful applications or for other fraudulent activity could damage our reputation, and we may face liability for unauthorized, inaccurate or fraudulent information distributed via our platform.
•: We have experienced losses in the past, and we may not achieve or sustain profitability in the future.
•: Our future quarterly results may fluctuate significantly, and if we fail to meet the expectations of analysts or investors, our stock price and the value of your investment could decline substantially.

Corporate Information

We were incorporated in Delaware in July 2009. Our principal executive offices are located at 1801 California Street, Suite 500, Denver, CO 80202, and our telephone number is (888) 985-7363.

Our website address is http://sendgrid.com. The information contained on our website is not incorporated by reference into this prospectus, and you should not consider any information contained on, or that can be accessed through, our website as part of this prospectus.

"SendGrid," the SendGrid logo and other trademarks or service marks of SendGrid appearing in this prospectus are our property. This prospectus contains additional trade names, trademarks, and service marks of other companies, which are the property of their respective owners. We do not intend our use or display of other companies' trade names, trademarks, or service marks to imply a relationship with, or endorsement or sponsorship of us by, these other companies.

Implications of Being an Emerging Growth Company

The Jumpstart Our Business Startups Act, or the JOBS Act, was enacted in April 2012 with the intention of encouraging capital formation in the United States and reducing the regulatory burden on newly public companies that qualify as "Emerging Growth Companies." We are an emerging growth company within the meaning of the JOBS Act. As an emerging growth company, we may take advantage of certain exemptions from various public reporting requirements, including the requirement that our internal control over financial reporting be audited by our independent registered public accounting firm pursuant to Section 404 of the Sarbanes-Oxley Act of 2002, certain requirements related to the disclosure

of executive compensation in this prospectus and in our periodic reports and proxy statements, and the requirement that we hold a nonbinding advisory vote on executive compensation and any golden parachute payments. We may take advantage of these exemptions until we are no longer an emerging growth company. Section 107 of the JOBS Act provides that an "emerging growth company" can take advantage of the extended transition period provided in Section 7(a)(2)(B) of the Securities Act of 1933, as amended, or the Securities Act, for complying with new or revised accounting standards. In other words, an "emerging growth company" can delay the adoption of certain accounting standards until those standards would otherwise apply to private companies.

We have elected to take advantage of the extended transition period to comply with new or revised accounting standards and to adopt certain of the reduced disclosure requirements available to emerging growth companies. As a result of the accounting standards election, we will not be subject to the same implementation timing for new or revised accounting standards as other public companies that are not emerging growth companies, which may make comparison of our financials to those of other public companies more difficult. Additionally, because we have taken advantage of certain reduced reporting requirements, the information contained herein may be different from the information you receive from other public companies in which you hold stock.

We will remain an emerging growth company until the earliest to occur of (i) the last day of the fiscal year in which we have more than $1.07 billion in annual revenue; (ii) the date we qualify as a "large accelerated filer," with at least $700 million of equity securities held by non-affiliates; (iii) the date on which we have issued, in any three-year period, more than $1.0 billion in non-convertible debt securities; and (iv) the last day of the fiscal year ending after the fifth anniversary of the completion of our initial public offering.

For certain risks related to our status as an emerging growth company, see "Risk Factors—Risks Related to this Offering and Ownership of Our Common Stock—We are an 'emerging growth company,' and we cannot be certain if the reduced disclosure requirements applicable to emerging growth companies will make our common stock less attractive to investors."

THE OFFERING


Common stock		7,700,000 shares
Over-allotment option		1,155,000 shares
Common stock to be outstanding after this offering		40,291,661 shares (41,446,661 shares, if the underwriters exercise their over-allotment option in full)
Use of proceeds		We estimate that the net proceeds from the sale of shares of our common stock that we are selling in this offering will be approximately $100.3 million (or approximately $115.9 million if the underwriters' over-allotment option to purchase additional shares in this offering is exercised in full), based upon an assumed initial public offering price of $14.50 per share, which is the midpoint of the estimated offering price range set forth on the cover page of this prospectus, and after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us.
		We intend to use the net proceeds we receive from this offering for working capital and other general corporate purposes. We may also use a portion of the net proceeds to make acquisitions or strategic investments, although we do not have any plans for such acquisitions or investments. See the section titled "Use of Proceeds" for additional information.
Proposed purchase by certain existing stockholders		Certain of our existing stockholders associated with Bessemer Venture Partners, which is an affiliate of a member of our board of directors, have indicated an interest in purchasing shares of common stock with an aggregate price of up to $10.0 million in this offering. Because these indications of interest are not binding agreements or commitments to purchase, the underwriters may elect to sell fewer or no shares in this offering to such stockholders, or these stockholders may elect to purchase fewer or no shares in this offering. The underwriters will receive the same discount from shares of our common stock purchased by such stockholders as they will from other shares of our common stock sold to the public in this offering. Any shares purchased by such stockholders will be subject to lock-up restrictions (with certain exceptions) described in the section entitled "Underwriters."


Concentration of Ownership		Our officers, directors and their affiliated funds and each of our stockholders who own greater than 5% of our outstanding common stock and their affiliates, in the aggregate, will beneficially own an aggregate of approximately 66.5% of our outstanding common stock following this offering, assuming no exercise of the underwriters' option to purchase additional shares. If the existing stockholders associated with Bessemer Venture Partners, which is an affiliate of a member of our board of directors, purchase shares of our common stock with an aggregate price of $10.0 million in this offering (the maximum indicated interest, as described above), assuming no exercise of the underwriters' option to purchase additional shares, our officers, directors and their affiliated funds and each of our stockholders who own greater than 5% of our outstanding common stock and their affiliates, in the aggregate, will beneficially own an aggregate of approximately 68.1% of our outstanding common stock following this offering, assuming an initial public offering price of $14.50 per share, which is the midpoint of the estimated offering price range set forth on the cover page of this prospectus. As a result, if some of these persons or entities act together, they will have significant influence over the outcome of matters submitted to our stockholders for approval.
New York Stock Exchange symbol		"SEND"

The number of shares of our common stock that will be outstanding after this offering is based on 32,591,661 shares of our common stock outstanding as of September 30, 2017, and excludes:

•

11,592,000 shares of our common stock issuable upon the exercise of stock options outstanding as of September 30, 2017, with a weighted average exercise price of $3.98 per share;

•

54,269 shares of our common stock issuable upon conversion of shares of our convertible preferred stock that are subject to an outstanding warrant as of September 30, 2017, with an exercise price of $2.764 per share;

•

466,571 shares of our common stock reserved for issuance to fund and support the operations of SendGrid.org, of which none were issued and outstanding as of September 30, 2017;

•

617,455 shares of our common stock issuable upon the vesting and settlement of Restricted Stock Units, or RSUs, outstanding as of September 30, 2017;

•

2,973,675 shares of our common stock reserved and available for future issuance under our 2017 Equity Incentive Plan, or 2017 Plan, which will become effective immediately prior to the date of the underwriting agreement for this offering (as more fully described in the section titled "Executive Compensation—Equity Incentive Plans"), as well as:

•: an aggregate of 728,145 shares of our common stock reserved for future grants under our 2012 Equity Incentive Plan, or 2012 Plan, as of October 27, 2017, which will be added to the shares reserved under our 2017 Plan upon its effectiveness, plus
•: any shares of our common stock issuable upon the exercise or settlement of outstanding stock awards under our 2012 plan and 2009 plan that will be added to our 2017 plan available reserve upon expiration or termination of such awards, plus

•: any automatic increases in the number of shares of our common stock reserved for future issuance under our 2017 Plan; and

•: 791,833 shares of our common stock reserved for issuance under our 2017 Employee Stock Purchase Plan, or 2017 ESPP, which will become effective immediately prior to the date of the underwriting agreement for this offering and contains provisions that automatically increase its share reserve each year, as more fully described in the section titled "Executive Compensation—Equity Incentive Plans."

The number of shares of our common stock that will be outstanding after this offering also excludes 34,717 shares of common stock issuable upon the vesting and settlement of RSUs that we granted on October 2, 2017 and 582,195 shares of common stock issuable upon the exercise of outstanding stock options that we granted at an exercise price of $12.72 per share on October 2, 2017.

Except as otherwise indicated, all information in this prospectus assumes:

•: the conversion of all outstanding shares of our convertible preferred stock into an aggregate of 24,535,227 shares of our common stock immediately upon the closing of this offering;
•: the conversion of an outstanding warrant to purchase shares of our convertible preferred stock into a warrant to purchase 54,269 shares of our common stock immediately upon the closing of this offering;
•: no exercise of outstanding stock options or the outstanding warrant and no settlement of outstanding RSUs after September 30, 2017;
•: the filing and effectiveness of our amended and restated certificate of incorporation and the effectiveness of our amended and restated bylaws, each of which will occur in connection with the closing of this offering; and
•: no exercise by the underwriters of their option to purchase up to an additional 1,155,000 shares of our common stock from us to cover over-allotments.

SUMMARY CONSOLIDATED FINANCIAL DATA

The following tables summarize our historical consolidated financial data. We have derived the historical consolidated statements of operations data for the years ended December 31, 2014, 2015, and 2016, from our audited consolidated financial statements included elsewhere in this prospectus. We have derived the historical consolidated statements of operations data for the nine months ended September 30, 2016 and 2017, and the historical consolidated balance sheet data as of September 30, 2017, from our unaudited interim consolidated financial statements included elsewhere in this prospectus. In management's opinion, we have prepared our unaudited interim consolidated financial statements on the same basis as our audited consolidated financial statements and have included all adjustments, which include only normal recurring adjustments, necessary to state fairly the financial information set forth in those statements. The following summary consolidated financial data should be read in conjunction with the section titled "Management's Discussion and Analysis of Financial Condition and Results of Operations" and our consolidated financial statements and related notes included elsewhere in this prospectus. Our historical results are not necessarily indicative of the results that may be expected in the future and our results for the nine months ended September 30, 2017, are not necessarily indicative of the results that may be expected for the full year or any other period.

	For the Year Ended December 31,									For the Nine Months Ended September 30,

	2014			2015			2016			2016			2017
	(In thousands, except per share amounts)
Consolidated Statements of Operations Data:
Revenue	$	42,776		$	58,476		$	79,929		$	56,858		$	80,159
Cost of revenue		15,187			18,961			21,605			15,995			21,357

Gross profit		27,589			39,515			58,324			40,863			58,802

Operating expenses:
Research and development		15,290			18,959			21,178			15,632			21,208
Selling and marketing		15,260			13,737			21,800			15,311			20,582
General and administrative		9,550			12,477			18,920			13,091			21,222
Loss on disposal of assets		63			1			27			27			2

Total operating expenses		40,163			45,174			61,925			44,061			63,014

Loss from operations		(12,574	)		(5,659	)		(3,601	)		(3,198	)		(4,212	)
Other income (expense), net		(386	)		(195	)		(307	)		(285	)		(515	)
Net loss before provision for income taxes		(12,960	)		(5,854	)		(3,908	)		(3,483	)		(4,727	)
Provision for income taxes		—			—			—			—			—

Net loss	$	(12,960	)	$	(5,854	)	$	(3,908	)	$	(3,483	)	$	(4,727	)



Weighted average shares used in computing net loss per share, basic and diluted⁽¹⁾		5,194			7,091			7,521			7,496			7,938
Net loss per share, basic and diluted⁽¹⁾	$	(2.50	)	$	(0.83	)	$	(0.52	)	$	(0.46	)	$	(0.60	)



Pro forma weighted average shares outstanding (unaudited)⁽¹⁾								29,921						32,473
Pro forma net loss per share (unaudited)⁽¹⁾							$	(0.13	)				$	(0.13	)



Other Data:
Adjusted net income (loss)⁽²⁾		(12,190	)		(4,460	)		(1,440	)		(1,832	)		1,217
Free cash flow⁽³⁾		(13,584	)		(3,965	)		(2,462	)		(1,160	)		233

(1): See Notes 2 and 13 to our consolidated financial statements for an explanation of the method used to calculate basic and diluted and pro forma net loss per common share attributable to common stockholders.

(2): We define adjusted net income (loss) as U.S. generally accepted accounting principles (GAAP) net income (loss), excluding stock-based compensation expense, restructuring expense, costs associated with mergers and acquisitions, warrant interest expense and non-capitalizable costs associated with this initial public offering. For more information about our adjusted net income (loss) and a reconciliation of our adjusted net income (loss) to net income (loss), the most directly comparable financial measure calculated and presented in accordance with GAAP, see the section titled "Selected Consolidated Financial Data."
(3): We define free cash flow as GAAP net cash flows from operating activities, reduced by purchase of property and equipment, and principal payments on capital lease obligations. For more information about our free cash flow and a reconciliation of our free cash flow to net cash flows from operating activities, the most directly comparable financial measure calculated in accordance with GAAP, see the section titled "Selected Consolidated Financial Data."

	As of September 30, 2017

	Actual			Pro Forma⁽¹⁾		Pro Forma As Adjusted⁽²⁾⁽³⁾
	(In thousands)
Consolidated Balance Sheet Data:
Cash and cash equivalents	$	37,397		$	37,397	$	137,682
Working capital		29,955			29,955		130,240
Property and equipment, net		26,322			26,322		26,322
Total assets		79,748			79,748		180,033
Convertible preferred stock warrant liability		635			—		—
Convertible preferred stock		80,688			—		—
Total stockholders' equity (deficit)		(38,999	)		42,324		142,609

(1): The pro forma column in the consolidated balance sheet data table above reflects (i) the automatic conversion of all outstanding shares of our convertible preferred stock as of September 30, 2017, into an aggregate of 24,535,227 shares of our common stock, which conversion will occur immediately upon the closing of this offering, (ii) the conversion of an outstanding warrant to purchase shares of our convertible preferred stock into a warrant to purchase 54,269 share of our common stock upon the closing of this offering, and (iii) the resulting classification of the preferred stock warrant liability to additional paid-in capital, as if such conversion and reclassification had occurred on September 30, 2017.
(2): The pro forma as adjusted column gives effect to (i) the pro forma adjustments set forth above and (ii) the sale and issuance by us of 7,700,000 shares of our common stock in this offering at the assumed initial public offering price of $14.50 per share, which is the midpoint of the estimated offering price range set forth on the cover page of this prospectus, after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us.
(3): Each $1.00 increase or decrease in the assumed initial public offering price of $14.50 per share, which is the midpoint of the estimated offering price range set forth on the cover page of this prospectus, would increase or decrease the pro forma as adjusted amount of each of cash and cash equivalents, working capital, total assets, and total stockholders' equity (deficit) by approximately $7.2 million, assuming that the number of shares offered by us, as set forth on the cover page of this prospectus, remains the same and after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us. We may also increase or decrease the number of shares we are offering. Each 1,000,000 share increase or decrease in the number of shares offered by us would increase or decrease the pro forma as adjusted amount of each of cash and cash equivalents, working capital, total assets and total stockholders' equity (deficit) by approximately $13.5 million, assuming that the assumed initial offering price of $14.50 remains the same, and after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us.

An investment in our common stock involves a high degree of risk. You should carefully consider the risks and uncertainties described below before making a decision to invest in our common stock. Our business, operating results, financial condition or prospects could be materially and adversely affected by any of these risks and uncertainties. In that case, the trading price of our common stock could decline and you might lose all or part of your investment. In addition, the risks and uncertainties discussed below are not the only ones we face. Our business, operating results, financial condition or prospects could also be harmed by risks and uncertainties not currently known to us or that we currently do not believe are material, and these risks and uncertainties could result in a complete loss of your investment. In assessing the risks and uncertainties described below, you should also refer to the other information contained in this prospectus (as supplemented or amended), including our consolidated financial statements and the related notes thereto, before making a decision to invest in our common stock.

Our recent growth may not be indicative of our future growth and, if we continue to grow, we may not be able to manage our growth effectively.

We have recently experienced a period of rapid growth in our headcount and operations. In particular, we grew from 58 employees as of December 31, 2011, to 408 fulltime employees as of September 30, 2017, and we have also significantly increased the number of emails processed by our platform over the last several years. We anticipate that we will continue to significantly expand our operations and headcount in the near term. Our growth has placed, and future growth will place, a significant strain on our management, technical, administrative, operational and financial infrastructure. Our success will depend in part on our ability to manage this growth effectively. To manage the expected growth of our operations and personnel, we will need to continue to improve our management, technical, administrative, operational and financial controls and our reporting systems and procedures. Failure to effectively manage our growth could result in difficulty or delays in effectively scaling our platform to handle increased email volumes, declines in quality or customer satisfaction, increases in costs, difficulties in introducing new features or other operational difficulties. Any of these difficulties could adversely impact our business and results of operations.

If we are unable to sustain our revenue growth rate, we may not achieve or maintain profitability in the future.

We have experienced rapid revenue growth over recent years, with revenue of $42.8 million, $58.5 million and $79.9 million in 2014, 2015 and 2016, respectively. Although we have experienced rapid revenue growth historically, we may not continue to grow as rapidly in the future and our revenue growth rates may decline. Any success that we may experience in the future will depend in large part on our ability to, among other things:

If we are unable to maintain consistent revenue or revenue growth, our stock price could be volatile or decline, and we may not achieve or maintain profitability. You should not rely on our revenue for any prior quarterly or annual periods as any indication of our future revenue or revenue growth.

If we are unable to attract new customers, retain existing customers or increase sales both to new and existing customers, our business and results of operations will be affected adversely.

To succeed, we must continue to attract and retain customers and increase sales to new and existing customers. We price our services on a tiered subscription model based on the customer's use of our services (principally, email volumes), and therefore the revenue we generate from our customers depends on their use of our services. We have only a limited salesforce and to date have relied primarily on our self-service model to generate our revenue. The amount that new and existing customers purchase, renew and use our services depends on a number of factors, including those outside of our control.

We may fail to attract new customers, retain existing customers or increase sales to new or existing customers as a result of a number of factors, including: reductions in our current or potential customers' spending levels; competitive factors affecting the cloud-based business software market, including the introduction of competing platforms, discount pricing and other strategies that may be implemented by our competitors; our ability to execute on our growth strategy and operating plans; a decline in our customers' level of satisfaction with our platform and customers' usage of our platform or an increased perception by our customers' that they can manage their email distribution and marketing efforts internally or otherwise without use of our platform; reductions in the use of email as a digital communication channel; the difficulty and cost to switch to a competitor may not be significant for many of our customers; changes in our relationships with third parties, including our strategic partners and payment processors; the timeliness and success of new services and functionality we may offer now or in the future, including our Marketing Campaigns service that we introduced in late 2015; concerns relating to actual or perceived security breaches; the frequency and severity of any system outages; and technological changes or problems. In addition, we believe a relatively small number of businesses have more than one unique paying account with us, and we count each of these accounts as a separate customer. We believe our number of customers is an important measure for evaluating our business. Because some businesses have more than one unique paying account with us and we count each of these accounts as a separate customer, the number of our customers set forth in this prospectus for any period is not necessarily indicative of the number of unique businesses from which we received revenue during any such period. We rely on our reputation and recommendations from key customers in order to promote our platform. The loss of any of our key customers could have a significant impact on our business reputation and our ability to obtain new customers. In addition, acquisitions of our customers could lead to cancellation of our contracts with those customers or by the acquiring companies.

Failure to attract new customers, retain existing customers or increase sales to customers will harm our business and results of operations.

Our limited operating history in new and developing markets and our rapid growth make it difficult to evaluate our current business and future prospects.

We introduced our Email API service in 2009, our Marketing Campaigns service in late 2015 and our Expert Services in 2016. The majority of our revenue growth has occurred in the last few years and was derived from the sale of subscriptions to our Email API service. This short operating history and our rapid growth make it difficult to evaluate our future prospects. Our ability to forecast our future operating results is subject to a number of uncertainties, including our ability to plan for and model future growth, particularly with respect to our most recently introduced services. If our assumptions regarding these uncertainties are incorrect or change in reaction to changes in our markets, or if we do not address these risks successfully, our operating and financial results could differ materially from our historical and expected operating and financial results, our business could suffer and the trading price of our stock may decline.

We also operate in new and developing markets that may not continue to develop as we expect. You should consider our future prospects in light of the challenges and uncertainties that we face, including the

fact that our business has grown rapidly and it may not be possible to discern fully the trends that we are subject to, that we operate in new and developing markets and that elements of our business strategy are new and subject to ongoing development. We have encountered and will continue to encounter risks and difficulties frequently experienced by growing companies in rapidly changing industries, including increasing and unforeseen expenses as we continue to grow our business. If we do not manage these risks successfully, our business and results of operations will be harmed.

If we are unable to increase adoption of our platform through our self-service model, our business, results of operations and financial condition may be adversely affected.

Historically, we have relied on the adoption of our platform through our self-service model for a significant majority of our revenue. We have only a limited salesforce. Although we believe our business model can continue to scale without a significantly larger salesforce, our self-service model may not continue to be as effective as we anticipate, and the absence of a large direct sales function may impede our future growth.

As we continue to scale our business, we may choose to invest in a larger direct salesforce to reach additional customers and grow our revenue. Our ability to manage a larger direct salesforce is uncertain. Identifying and recruiting additional qualified sales personnel and managing and training them once hired would require significant time, expense and attention and would significantly impact our business model. In addition, adding additional salesforce would considerably change our cost structure and results of operations, and we may have to reduce other expenses, such as our research and development expense, in order to accommodate a corresponding increase in marketing and sales expense and attain and maintain profitability. If our lack of a large direct salesforce limits us from reaching additional customers and growing our revenue and we are unable to hire, develop and retain talented sales personnel in the future, our revenue growth and results of operations may be harmed.

Our growth depends in part on the success of our strategic relationships with third parties to sell our services.

We have established strategic relationships with a number of other companies, including public cloud infrastructure providers and ecommerce platforms, software vendors that offer complementary products and with which we co-sell our services and digital marketing agencies that resell our services to their clients. In order to grow our business, we anticipate that we will continue to establish and maintain these strategic relationships. Identifying strategic partners, and negotiating and documenting relationships with them, requires significant time and resources. Our competitors may be effective in providing incentives to third parties to favor their products or services over ours or to prevent or reduce subscriptions to our platform. In addition, acquisitions of our strategic partners by our competitors, or acquisition of our competitors by our strategic partners, could result in a decrease in the number of our current and potential customers, as our strategic partners may no longer facilitate the adoption of our platform by potential customers.

If we are unsuccessful in establishing or maintaining our strategic relationships with third parties, our ability to compete or to grow our revenues could be impaired and our operating results could suffer. Even if we are successful in our strategic relationships, we cannot assure you that these relationships will result in increased usage of our services or increased revenues.

Our future success depends in part on our ability to continue to drive adoption of our platform and services by international customers, and our international operations and sales to customers with international operations expose us to risks inherent in international sales.

We generated more than 36% of our revenue in each of the last three years from customers located outside the United States. The future success of our business will depend, in part, on our ability to continue to expand our customer base worldwide and to sell additional services to international customers.

If we are unable to successfully market our platform to or localize our services for international customers, then our business, results of operations and financial condition may be adversely affected and our growth may be constrained.

We have limited experience operating in international markets where the challenges of conducting our business can be significantly different from those we have faced in the United States and the existing markets in which we operate and where business practices may create internal control risks. We have only recently established operations outside of the United States, with the opening of an office in London. We may open additional non-U.S. offices in the future. There are a number of risks inherent in conducting international business, including:

If we are unable to effectively manage these risks, our relationships with our existing and prospective customers, strategic partners and employees and our operations outside of the United States may be adversely affected.

If we are not able to maintain and enhance our brand and maintain and increase market awareness of our company and services, then our business, results of operations and financial condition may be adversely affected.

We believe that maintaining and enhancing the "SendGrid" brand identity and maintaining and increasing market awareness of our company and services is critical to achieving widespread acceptance of our platform, to strengthen our relationships with our existing customers and to our ability to attract new customers. The successful promotion of our brand will depend largely on our continued marketing efforts, our ability to continue to offer high quality services, our ability to be thought leaders in our industry and our ability to successfully differentiate our platform and services from competing products and services. For example, we rely on both algorithmic and purchased listings displayed by search engines to attract a

significant percentage of the customers. Algorithmic listings cannot be purchased, and instead are determined and displayed solely by a set of formulas designed by the search engine. Purchased listings can be purchased by advertisers in order to attract customers to their websites, but the cost of purchased search listing advertising may increase as demand for these channels grows. If search engines on which we rely for algorithmic listings modify their algorithms in an attempt to optimize their search listings, this could result in fewer potential customers clicking through to our website, requiring us to resort to additional purchased listings or other costly advertisements to attempt to replace this traffic. If one or more search engines on which we rely for purchased listings modifies or terminates its relationship with us, or increases the amounts it charges us, our expenses could rise. Any such increases could negatively affect market awareness of our brand and our business, results of operations and financial condition.

In addition, independent industry analysts often provide reviews of our services and competing products and services, which may significantly influence the perception of our services in the marketplace. If these reviews are negative or not as strong as reviews of our competitors' products and services, then our brand may be harmed. This may cause us to lose existing customers, decrease the number of new customers that we are able to attract or lower our pricing model, each of which would likely harm our results of operations.

From time to time, our customers and other third parties have complained about our platform, such as complaints about our pricing and customer support or the use of our platform to transmit spam, phishing scams, website links to harmful applications or other harmful or illegal material. If we do not handle customer and other complaints effectively, then our brand and reputation may suffer, our customers may lose confidence in us and our customers may reduce or cease their use of our services. In addition, many of our customers post about and discuss Internet-based products and services, including our platform and services, on social media. Our success depends, in part, on our ability to generate positive customer feedback and minimize negative feedback on social media channels where existing and potential customers seek and share information. If actions we take or changes we make to our platform or services, particularly as our platform continues to scale, upset these customers then their online commentary could negatively affect our brand and reputation. Complaints or negative publicity about us, our platform or our services could materially and adversely impact our ability to attract and retain customers, our business, results of operations and financial condition.

The promotion of our brand also requires us to make substantial expenditures, and we anticipate that these expenditures will increase as our market becomes more competitive and as we expand into new markets. To the extent that these activities increase revenue, this revenue still may not be enough to offset the increased expenses we incur. If we do not successfully maintain and enhance our brand, then our business may not grow, we may see our pricing power reduced relative to competitors and we may lose customers, all of which would adversely affect our business, results of operations and financial condition.

The market in which we participate is highly competitive and, if we do not compete effectively, our operating results could be harmed.

We provide cloud-based services that enable businesses to reach their customers using email for both transactional and marketing purposes. The market for providing these services is fragmented, with some vendors addressing transactional email services, some vendors addressing email marketing services and other vendors providing a broad array of services that include transactional and marketing services as part of a software suite or broader portfolio of software offerings. Notwithstanding the availability of third-party software services, some businesses rely on internally-developed solutions for their email communications needs. The market for digital communications services is rapidly evolving, creating opportunity for new competitors to enter the market with point product solutions or addressing specific

segments of the market. In addition, in some instances, we have strategic or other commercial relationships with companies with which we also compete, such as Amazon Web Services. Our competitors include:

We believe the principal factors on which we compete include: completeness of offering; credibility with developers and marketers; global reach; ease of adoption; features and functionality; platform scalability, reliability, security and performance; brand awareness and reputation; integration with third-party applications and data sources; customer support; and the total cost of deployment and ownership. Our current and potential competitors may develop and market new technologies with similar or superior functionality to our platform or at a cheaper price point that render our existing or future services less competitive or obsolete, and we may need to decrease the prices or accept less favorable terms for subscriptions for our services in order to remain competitive. If we are unable to maintain our pricing due to competitive pressures, our margins will be reduced and our operating results will be negatively affected.

Our current and potential competitors also may have significantly more financial, technical, marketing and other resources than we have, may be able to devote greater resources to the development, promotion, sale and support of their products and services, may have more extensive customer bases and broader customer relationships and may have longer operating histories and greater name recognition. As a result, these competitors may respond faster to new technologies and undertake more extensive marketing programs for their products or services. If these companies decide to further invest in and develop, market or resell competitive products or services, or acquire or form a strategic alliance with one of our other competitors, our ability to compete effectively could be significantly compromised and our operating results could be harmed. In a few cases, these vendors may offer competitive products or services at little or no additional cost by bundling it with their existing suite of applications. To the extent any of our competitors has existing relationships with potential customers for either email software or other applications, those customers may be unwilling to purchase our platform because of their existing relationships with our competitor. If we are unable to compete with such companies, the demand for our platform and services could substantially decline.

If our security measures are breached or unauthorized access to our or our customers' and their end customers' private or proprietary data is otherwise obtained, our platform or services may be perceived as not being secure, our reputation may be severely harmed, customers may reduce the use of or stop using our services, we may incur significant liabilities and we may lose the ability to offer our customers a credit card payment option.

Our operations involve the storage and transmission of data of our customers and their end customers, including personally identifiable information. Security breaches or other incidents could result in unauthorized access to, loss of or unauthorized disclosure of this information, litigation, indemnity obligations and other possible liabilities, as well as negative publicity, which could damage our reputation, impair our sales and harm our customers and our business. Cyberattacks and other malicious Internet-based activity continue to increase generally, and cloud-based service providers like us are regularly targeted. For example, in 2013, we suffered a distributed denial of service attack, whereby a cybercriminal gained access to our webpage and, in 2015, a cybercriminal gained unauthorized access to several of our internal systems, including those containing sensitive and confidential customer data. It is possible that we may face increased risk of cybersecurity attacks as compromising our platform may allow cybercriminals to send a large number of phishing emails that bypasses end users' spam filters. If our security measures are compromised as a result of third-party action, employee or customer error, malfeasance, stolen or fraudulently obtained log-in credentials or otherwise, our reputation could be damaged, our business may be harmed and we could incur significant liability. In addition, if the security measures of our customers

are compromised, even without any actual compromise of our own systems, we may face negative publicity or reputational harm if our customers or anyone else incorrectly attributes the blame for such security breaches to us or our systems. We may be unable to anticipate or prevent techniques used to obtain unauthorized access or to sabotage our systems because they change frequently and generally are not detected until after an incident has occurred. As we increase our customer base and our brand becomes more widely known and recognized, we may become more of a target for third parties seeking to compromise our security systems or gain unauthorized access to our customers' data. Further, as we rely more on third-party and public-cloud infrastructure, such as Amazon Web Services, we will become more dependent on third-party security measures to protect against unauthorized access, cyberattacks and the mishandling of customer data. Any security breach, whether actual or perceived, would harm our reputation, and we could lose customers and fail to acquire new customers. In addition, many governments have enacted laws requiring companies to notify individuals of data security incidents involving certain types of personal data and any mandatory disclosures we may make regarding a security breach would likely lead to widespread negative publicity, which may cause our customers to lose confidence in the effectiveness of our data security measures. It is also possible that security breaches sustained by our competitors could result in negative publicity for our entire industry that indirectly harms our reputation and diminishes demand for our services.

Furthermore, failure to maintain compliance with the data protection policy standards adopted by the major credit card issuers and other payment processors may limit our ability to offer our customers a credit card or online payment option. Any loss of our ability to offer our customers a credit card payment or online payment option would harm our reputation and make our platform and services less attractive to many organizations by negatively impacting our customer experience and significantly increasing our administrative costs related to customer payment processing.

Our existing general liability insurance may not cover any, or cover only a portion of any, potential claims related to security breaches to which we are exposed or may not be adequate to indemnify us for all or any portion of liabilities that may be imposed. In addition, there can be no assurance that the limitations on liability in our contracts would be enforceable or adequate or would otherwise protect us from any such liabilities with respect to any particular claim. Any imposition of liability that is not covered by insurance or is in excess of insurance coverage would increase our operating expenses and reduce our net income.

Our customers' and other users' violation of our policies or other misuse of our platform to transmit offensive or illegal messages, phish, spam, website links to harmful applications or for other fraudulent activity could damage our reputation, and we may face liability for unauthorized, inaccurate or fraudulent information distributed via our platform.

Despite our ongoing and substantial efforts to limit such use, a portion of our customers use our platform to transmit offensive or illegal messages, spam, phishing scams and website links to harmful applications, reproduce and distribute copyrighted material or the trademarks of others without permission, and report inaccurate or fraudulent data or information. These issues also arise with respect to a portion of those users who use our platform on a free trial basis. These actions are in violation of our policies. However, our efforts to defeat spamming attacks and other fraudulent activity will not prevent all such attacks and activity, such use of our platform could damage our reputation and we could face claims for damages, copyright or trademark infringement, defamation, negligence or fraud. Moreover, our customers' and other users' promotion of their products and services through our platform might not comply with federal, state and foreign laws. We rely on contractual representations made to us by our customers that their use of our platform will comply with our policies and applicable law, including, without limitation, our email policy. Although we retain the right to verify that customers and other users are abiding by our email policy and to review their email and email lists, our customers and other users are ultimately responsible for compliance with our policies, and we do not systematically audit our customers or other users to confirm compliance with our policies. We cannot predict whether our role in facilitating

our customers' or other users' activities would expose us to liability under applicable law. Even if claims asserted against us do not result in liability, we may incur substantial costs in investigating and defending such claims. If we are found liable for our customers' or other users' activities, we could be required to pay fines or penalties, redesign business methods or otherwise expend resources to remedy any damages caused by such actions and to avoid future liability.

Real or perceived errors, failures, vulnerabilities or bugs in our software could adversely affect our business, results of operations, financial condition and growth prospects.

Our platform is complex, and therefore, undetected errors, failures or bugs may occur, particularly as we continue to scale our platform to accommodate future growth. Our platform may be used in IT environments with different operating systems, system management software, applications, devices, databases and equipment and networking configurations, which may cause errors or failures of our platform or other aspects of the IT environment into which it is deployed. Despite testing by us, errors, failures or bugs may not be found until our platform is used by our customers. Real or perceived errors, failures or bugs in our platform or services could result in negative publicity, loss of or delay in market acceptance of our platform or services, weakening of our competitive position, claims by customers for losses sustained by them or failure to meet any stated service level commitments in our customer agreements. For example, in May 2017, we experienced an error with a database that stores customers' Marketing Campaigns contact information that resulted in delayed email sending for several hours. Correcting any of these problems could require significant expenditures of our capital and other resources and could cause interruptions, delays or cessation in the sale of our services, which could cause us to lose existing or potential customers and adversely affect our business, results of operations, and financial condition.

Our platform and services and our business are subject to a variety of U.S. and international laws and regulations, including those regarding privacy, data protection and information security. Any failure by us or our third-party service providers, as well as the failure of our platform or services to comply with applicable laws and regulations would harm our business, results of operations and financial condition.

We are subject to a variety of laws and regulations, including regulation by various federal government agencies, including the U.S. Federal Trade Commission, or FTC, and state and local agencies. The United States and various state and foreign governments have adopted or proposed limitations on, or requirements regarding, the collection, distribution, use, security and storage of personally identifiable information of individuals, and the FTC and many state attorneys general are applying federal and state consumer protection laws to impose standards on the online collection, use and dissemination of data. Self-regulatory obligations, other industry standards, policies and other legal obligations may apply to our collection, distribution, use, security or storage of personally identifiable information or other data relating to individuals. In addition, the federal government and many states and foreign governments have enacted laws requiring companies to notify individuals of data security breaches involving certain types of personal data. These obligations may be interpreted and applied in an inconsistent manner from one jurisdiction to another and may conflict with one another, other regulatory requirements or our internal practices. Any failure or perceived failure by us to comply with United States, European Union or other foreign privacy or security laws, regulations, policies, industry standards or legal obligations or any security incident that results in the unauthorized access to, or acquisition, release or transfer of, personally identifiable information or other customer data may result in governmental enforcement actions, litigation, fines and penalties or adverse publicity and could cause our customers to lose trust in us, which could have an adverse effect on our reputation and business.

We expect that there will continue to be new proposed laws, regulations and industry standards concerning privacy, data protection and information security in the United States, the European Union and other jurisdictions, and we cannot yet determine the impact such future laws, regulations and

standards may have on our business. For example, in May 2018, the general data protection regulation, or GDPR, will come into force, bringing with it a complete overhaul of E.U. data protection laws: the new rules will supersede current E.U. data protection legislation, impose more stringent E.U. data protection requirements, and provide for greater penalties for noncompliance. Changing definitions of personal data and information may also limit or inhibit our ability to operate or expand our business, including limiting strategic partnerships that may involve the sharing of data. Also, some jurisdictions require that certain types of data be retained on servers within these jurisdictions. Our failure to comply with applicable laws, directives and regulations may result in enforcement action against us, including fines and imprisonment, and damage to our reputation, any of which may have an adverse effect on our business and operating results. Further, in October 2015, the European Court of Justice issued a ruling invalidating the U.S.-E.U. Safe Harbor Framework, which facilitated personal data transfers to the United States in compliance with applicable E.U. data protection laws. In July 2016, the European Union and the United States political authorities adopted the E.U.-U.S. Privacy Shield, or Privacy Shield, replacing the Safe Harbor Framework and providing a new mechanism for companies to transfer E.U. personal data to the United States. U.S. organizations wishing to self-certify under the Privacy Shield have to pledge their compliance with its seven core and sixteen supplemental principles, which are based on European Data Protection Law. We have assessed the requirements of Privacy Shield and are implementing changes internally in order to meet the requirements. We plan to complete this process, submit our application and become self-certified under the Privacy Shield, by the end of this year.

We publicly post our privacy policies and practices concerning our processing, use and disclosure of the personally identifiable information provided to us by our website visitors. Our publication of our privacy policies and other statements we publish that provide promises and assurances about privacy and security can subject us to potential state and federal action if they are found to be deceptive or misrepresentative of our practices.

If our service is perceived to cause, or is otherwise unfavorably associated with, violations of privacy or data security requirements, it may subject us or our customers to public criticism and potential legal liability. Existing and potential privacy laws and regulations concerning privacy and data security and increasing sensitivity of consumers to unauthorized processing of personal information may create negative public reactions to technologies, products and services such as ours. Public concerns regarding personal information processing, privacy and security may cause some of our customers' end users to be less likely to visit their websites or otherwise interact with them. If enough end users choose not to visit our customers' websites or otherwise interact with them, our customers could stop using our platform. This, in turn, may reduce the value of our services and slow or eliminate the growth of our business.

Evolving and changing definitions of what constitutes "Personal Information" and "Personal Data" within the European Union, the United States and elsewhere, especially relating to the classification of internet protocol, or IP, addresses, machine or device identification numbers, location data and other information, may limit or inhibit our ability to operate or expand our business. Future laws, regulations, standards and other obligations could impair our ability to collect or use information that we utilize to provide email delivery and marketing services to our customers, thereby impairing our ability to maintain and grow our customer base and increase revenue. Future restrictions on the collection, use, sharing or disclosure of our customers' data or additional requirements for express or implied consent of customers for the use and disclosure of such information limit our ability to develop new services and features.

United States federal legislation and the laws of many foreign countries impose certain obligations on the senders of commercial emails, which could minimize the effectiveness of our platform, and establish financial penalties for non-compliance, which could increase the costs of our business.

The Federal Controlling the Assault of Non-Solicited Pornography and Marketing Act of 2003, or the CAN-SPAM Act, establishes certain requirements for commercial email messages and transactional email messages and specifies penalties for the transmission of email messages that are intended to deceive the

recipient as to source or content. The CAN-SPAM Act, among other things, obligates the sender of commercial emails to provide recipients with the ability to opt out of receiving future commercial emails from the sender. In addition, some states have passed laws regulating commercial email practices that are significantly more restrictive and difficult to comply with than the CAN-SPAM Act. For example, Utah and Michigan prohibit the sending of email messages that advertise products or services that minors are prohibited by law from purchasing (e.g., alcoholic beverages, tobacco products, illegal drugs) or that contain content harmful to minors (e.g., pornography) to email addresses listed on specified child protection registries. Some portions of these state laws may not be preempted by the CAN-SPAM Act. In addition, certain foreign jurisdictions, such as Australia, Canada and the European Union, have enacted laws that regulate sending email, and some of these laws are more restrictive than U.S. laws. For example, some foreign laws prohibit sending broad categories of email unless the recipient has provided the sender advance consent to receipt of such email, or in other words has "opted-in" to receiving such email. If we were found to be in violation of the CAN-SPAM Act, applicable state laws governing email not preempted by the CAN-SPAM Act or foreign laws regulating the distribution of email, whether as a result of violations by our customers or our own acts or omissions, we could be required to pay large penalties, which would adversely affect our financial condition, significantly harm our business and injure our reputation. The terms of injunctions, judgments, consent decrees or settlement agreements entered into connection with enforcement actions or investigations against our company in connection with any of the foregoing laws may also require us to change one or more aspects of the way we operate our business, which could impair our ability to attract and retain customers or could increase our operating costs.

The standards that private entities and inbox service providers use to regulate the use and delivery of email have in the past interfered with, and may in the future interfere with, the effectiveness of our platform and our ability to conduct business.

Our customers rely on email to communicate with their existing or prospective customers. Various private entities attempt to regulate the use of email for commercial solicitation. These entities often advocate standards of conduct or practice that significantly exceed current legal requirements and classify certain email solicitations that comply with current legal requirements as spam. Some of these entities maintain "blacklists" of companies and individuals, and the websites, inbox service providers and IP addresses associated with those entities or individuals that do not adhere to those standards of conduct or practices for commercial email solicitations that the blacklisting entity believes are appropriate. If a company's IP addresses are listed by a blacklisting entity, emails sent from those addresses may be blocked if they are sent to any internet domain or internet address that subscribes to the blacklisting entity's service or uses its blacklist.

From time to time, some of our IP addresses have become, and we expect will continue to be, listed with one or more blacklisting entities due to the messaging practices of our customers and other users. We may be at an increased risk of having our IP addresses blacklisted due to our scale and volume of email processed, compared to our smaller competitors. While the overall percentage of such email solicitations that our individual customers send may be at or below reasonable standards, the total aggregate number of all emails that we process on behalf of our customers may trigger increased scrutiny from these blacklisting entities. There can be no guarantee that we will be able to successfully remove ourselves from those lists. Because we fulfill email delivery on behalf of our customers, blacklisting of this type could undermine the effectiveness of our customers' transactional email, email marketing programs and other email communications, all of which could have a material negative impact on our business and results of operations.

Additionally, inbox service providers can block emails from reaching their users. While we continually improve our own technology and work closely with inbox service providers to maintain our deliverability rates, the implementation of new or more restrictive policies by inbox service providers may make it more difficult to deliver our customers' emails, particularly if we are not given adequate notice of a change in

policy or struggle to update our platform or services to comply with the changed policy in a reasonable amount of time. In addition, some inbox service providers categorize as "promotional" emails that originate from email service providers and, as a result, direct them to an alternate or "tabbed" section of the recipient's inbox. If inbox service providers materially limit or halt the delivery of our customers' emails, or if we fail to deliver our customers' emails in a manner compatible with inbox service providers' email handling or authentication technologies or other policies, or if the open rates of our customers' emails are negatively impacted by the actions of inbox service providers to categorize emails, then customers may question the effectiveness of our platform and cancel their accounts. This, in turn, would harm our business and financial condition.

We are subject to governmental export controls and economic sanctions and anti-corruption laws and regulations that could impair our ability to compete in international markets and subject us to liability if we are not in compliance with applicable laws.

Various of our operations and services may be subject to export control and economic sanctions regulations, including the U.S. Export Administration Regulations, U.S. Customs regulations and various economic and trade sanctions regulations administered by the U.S. Treasury Department's Office of Foreign Assets Controls. The provision of our services must be made in compliance with these laws and regulations. Obtaining the necessary authorizations, including any required license, for a particular deployment may be time-consuming, is not guaranteed and may result in the delay or loss of sales opportunities. In addition, changes in our platform capabilities or services, or changes in applicable export or economic sanctions regulations may create delays in the introduction and deployment of our platform and services in international markets, or, in some cases, prevent the provision of our services to certain countries or end users. Any change in export or economic sanctions regulations, shift in the enforcement or scope of existing regulations, or change in the countries, governments, persons or technologies targeted by such regulations, could also result in decreased use of our platform and services, or in our decreased ability to provide our services to existing or prospective customers with international operations. Any decreased use of our platform and services or limitation on our ability to provide our services could adversely affect our business, results of operations and financial condition.

Furthermore, U.S. export control laws and economic sanctions prohibit the exportation of certain products and services to countries, territories, governments and persons targeted by U.S. sanctions. While we are currently taking precautions to prevent our platform from being accessed by persons targeted by U.S. sanctions, including IP address blocking, such measures may be circumvented. Given the technical limitations in developing measures that will prevent access to internet based services from particular geographies or by particular individuals, we have previously identified and expect we will continue to identify customer accounts for our platform and services that originate or that we suspect originate from countries that are subject to U.S. embargoes.

We are aware that trials of and subscriptions to our platform have been initiated by persons and organizations in countries that are the subject of U.S. embargoes. Our provision of services in these instances was likely in violation of trade sanctions laws. We have terminated the accounts of such persons and organizations as we have become aware of them. We filed an initial voluntary self-disclosure with the U.S. Department of Treasury's Office of Foreign Assets Control, or OFAC, in February 2016 concerning these potential violations and we filed a subsequent voluntary disclosure with OFAC concerning these potential violations in May 2017. We received and responded to questions from OFAC in July 2017. We cannot predict when OFAC will complete its review and determine whether any violations occurred or levy penalties.

Our failure to comply with U.S. sanctions or export control laws or regulations could cause us and certain of our employees to be subject to substantial civil or criminal penalties, including the possible loss of export privileges; fines, which may be imposed on us and responsible employees or managers; and, in extreme cases, the incarceration of responsible employees or managers. Each instance in which we allow

access to our platform may constitute a separate violation of these laws. We may also suffer reputational harm.

Further, we incorporate encryption technology into certain of our platform functions and services. Various countries regulate the import of certain encryption technology, including through import permitting and licensing requirements, and have enacted laws that could limit our customers' ability to import our services into those countries. Encryption products and the underlying technology may also be subject to export control restrictions. Governmental regulation of encryption technology and regulation of exports of encryption products, or our failure to obtain required approval for our services, when applicable, could harm our international sales and adversely affect our revenue. Compliance with applicable regulatory requirements regarding the provision of our services, including with respect to new services, may create delays in the introduction of our services in international markets, prevent our customers with international operations from deploying our platform and using our services throughout their globally-distributed systems or, in some cases, prevent the provision of our services to some countries altogether.

Additionally, we are subject to the Foreign Corrupt Practices Act, or FCPA, the U.K. Bribery Act and other anti-corruption, anti-bribery and anti-money laundering laws in various jurisdictions both domestic and abroad. We and our third-party business partners and intermediaries may have direct or indirect interactions with officials and employees of government agencies or state-owned or affiliated entities and may be held liable for the corrupt or other illegal activities of these third-party business partners and intermediaries, our employees, representatives, contractors, channel partners, and agents, even if we do not explicitly authorize such activities. While we have policies and procedures in place to address compliance with such laws, we cannot assure you that all of our employees and agents will not take actions in violation of our policies and applicable law, for which we may be ultimately held responsible. Any violation of the FCPA or other applicable anti-bribery, anti-corruption laws, and anti-money laundering laws could result in whistleblower complaints, adverse media coverage, investigations, loss of export privileges, severe criminal or civil sanctions, or suspension or debarment from U.S. government contracts, all of which may have an adverse effect on our reputation, business, operating results and prospects.

If we are unable to develop and release enhancements to our platform and services or new services and functionality to respond to rapid technological change in a timely and cost-effective manner, our business, operating results, and financial condition could be adversely affected.

The market for our platform and services is characterized by rapid technological change, frequent new product and service introductions and enhancements, changing customer demands, and evolving industry standards. The introduction of products and services embodying new technologies can quickly make existing products and services obsolete and unmarketable. For example, new Internet standards and technologies or new standards in the field of operating system support could emerge that are incompatible with customer deployments of our platform. The success of any enhancements or improvements to our platform or any new services or functionality depends on several factors, including timely completion, competitive pricing, adequate quality testing, integration with existing technologies and our platform, and overall market acceptance. We cannot be sure that we will succeed in developing, marketing and delivering on a timely and cost-effective basis enhancements or improvements to our platform or any services or functionality that respond to technological change or new customer requirements, nor can we be sure that any enhancements or improvements to our platform will achieve market acceptance. For example, we introduced our Marketing Campaigns service in late 2015 and the service may not achieve broad market acceptance or be cost-effective in the long term.

Further, our success depends on meeting customer demands and expectations both with respect to the ability of our API to integrate within their applications and the speed, reliability and effectiveness of our platform. For example, if we are unable to adapt our platform on a timely basis to new email or operating system protocols or we fail to effectively integrate our API with new technologies and standards, the ability

of our platform to integrate with our customers' systems or satisfy our customers' needs may be impaired. In addition, because we use both co-located data centers and public cloud resources to host our platform, we need to continually enhance and improve our platform to keep pace with changes in Internet-related hardware, software, communications, and database technologies and standards. As we transition to Amazon Web Services to host a portion of our platform, we will become more dependent on third parties to keep pace with such changes. If we cannot deliver technologically competitive services, we could lose customers and our revenues and stock price may decline.

Any new services or functionality that we develop may not be introduced in a timely or cost-effective manner, may contain errors or defects, or may not achieve the broad market acceptance necessary to generate sufficient revenue. Moreover, even if we introduce new services or functionality, we may experience a decline in revenue of our existing services that is not offset by revenue from the new services or functionality. For example, customers may delay making purchases of new services to permit them to make a more thorough evaluation of these services or until industry and marketplace reviews become widely available. In addition, we may lose existing customers that choose a competitor's products and services or that choose to rely on an internally-developed solution, rather than migrate to our new services. Similarly, if we offer a bundle of our services that our customers and prospective customers do not find compelling, our business will be harmed. This could result in a temporary or permanent revenue shortfall and adversely affect our business.

We may not be able to scale our technology infrastructure and platform quickly enough to meet our customers' growing needs and if we are not able to grow efficiently, our operating results could be harmed.

As usage of our platform grows, we will need to continue making significant investments to develop and implement new technologies in our infrastructure operations to support our growth. In addition, we will need to appropriately scale our internal business systems and our services organization, including basic customer support and our Expert Services team, to serve our growing customer base. Any failure of, or delay in, these efforts could impair the performance of our platform and reduce customer satisfaction and reduce our growth. Even if we are able to upgrade our systems and expand our staff, any such expansion may be expensive and complex. To the extent that we do not effectively scale our platform and infrastructure to meet the growing needs of our customers or are not able to manage that growth effectively, we may not be able to grow as quickly as we anticipate, our customers may reduce or stop use of our services, we may be unable to compete effectively and our business and operating results may be harmed.

We are primarily dependent on a single service, our Email API service, and the lack of continued market acceptance of our Email API service could cause our operating results to suffer.

Sales of our Email API service account for a substantial majority of our revenue. We expect that we will be substantially dependent on our Email API service to generate revenue for the foreseeable future. As a result, our operating results could suffer due to:

If the market for our Email API service grows more slowly than anticipated or if demand for our Email API service does not grow as quickly as anticipated, we may not be able to grow our revenue.

Our services are sold on a short-term basis, such that subscription renewal or usage rates can decrease rapidly, and if we do not accurately predict these rates, our future revenue and operating results may be harmed.

We charge our customers based on their use of our services. We generally enter into monthly subscription agreements with our customers and, therefore, most of our customers may reduce or cease their use of our services on a monthly basis without penalty or termination charges. Our retention of customers and our customers' use of our services are used to determine our subscription net dollar retention rate. We believe subscription net dollar retention rate is an important measure for evaluating our business. Additionally, our subscription agreements for use of our Email API service include a fixed fee that covers a specified number of email credits in the applicable month. If our customers lower the number of email credits they purchase in any month, then the fixed fees we charge will decrease. We have historically experienced customer turnover as a result of many of our customers being SMBs in the entrepreneurial stage of their development that are more susceptible than larger businesses to general economic conditions and other risks affecting their businesses. We cannot accurately predict customers' usage levels on a monthly basis and the loss of customers or reductions in their usage levels of our services may each have a negative impact on our business, results of operations and financial condition, including our subscription net dollar retention rate and our subscription gross dollar churn rate, which is a component of our subscription net dollar retention rate.

Any failure to offer high-quality support may harm our relationships with our customers and have a negative impact on our business and financial condition.

Our customers depend on our customer support team to resolve technical and operational issues relating to our platform. Our ability to provide effective customer support is largely dependent on our ability to attract, train, and retain qualified personnel with experience in supporting customers on platforms such as ours. Our customer base has grown significantly and that has and will put additional pressure on our customer support team. We may be unable to respond quickly enough to accommodate short-term increases in customer demand for support. We also may be unable to modify the scope and delivery of our support to compete with changes in the support provided by our competitors. Increased customer demand for support, without corresponding revenue, could increase costs and negatively affect our operating results. In addition, as we continue to grow our operations and expand internationally, we need to be able to provide efficient customer support that meets our customers' needs globally at scale and our customer support team will face additional challenges, including those associated with delivering support and documentation in languages other than English. If we are unable to provide efficient customer support globally at scale, our ability to grow our operations may be harmed and we may need to hire additional support personnel, which could negatively impact our operating results. In addition, we provide self-service support resources to our customers, such as our best practice guides and webcasts hosted on our website. We also rely on our user community to serve as a resource for questions on any part of our platform. Members of our user community are not obligated to participate in discussions with other users, and to the extent they do not our customers' ability to find answers to questions about our platform of services may suffer. If we are unable to develop self-service support resources that are easy to use and that our customers utilize to resolve their technical issues or if our customers choose not to take advantage of these self-service support services, customers may continue to direct support requests to our customer support team instead of relying on our self-service support resources and our customers' experience with our platform may be negatively impacted. Any failure to maintain high-quality support, or a market

perception that we do not maintain high-quality support, could harm our reputation, our ability to sell our services to existing and prospective customers, and our business, operating results, and financial condition.

To deliver our services, we rely on internet service providers for network connectivity and co-location facilities and public cloud infrastructure to host our platform.

We interconnect with internet service providers around the world to enable the use of our platform by our customers and we expect that we will continue to rely heavily on internet service providers for network connectivity going forward. Our reliance on internet service providers reduces our control over quality of service and exposes us to potential service outages and rate fluctuations. If a significant portion of our internet service providers stop providing us with access to their network infrastructure, fail to provide access on a cost-effective basis, cease operations, or otherwise terminate access, the delay caused by qualifying and switching to other internet service providers could be time consuming and costly and could adversely affect our business, results of operations and financial condition.

In addition, we currently serve the majority of our platform infrastructure from multiple co-located third-party data centers located throughout the United States and in certain international locations. We are in the process of transitioning the hosting of a portion of our platform infrastructure to Amazon Web Services. As a result, our operations depend, in part, on the ability of third parties to protect these facilities and resources against damage or interruption from natural disasters, power or network failures, criminal acts and similar events. In the event that any of our hosting arrangements are terminated, or if there is a lapse of service or damage to a facility or other resource, we could experience interruptions in our platform as well as delays and additional expenses in arranging new facilities and resources. We have experienced and expect that we will in the future experience such interruptions from time to time.

Any damage to, or failure of, the systems of our third-party providers could result in interruptions to and may cause errors or poor quality communications with our platform. Even with current and planned disaster recovery arrangements, our business could be harmed. Also, in the event of damage or interruption, our insurance policies may not adequately compensate us for any losses that we may incur. These factors in turn could further reduce our revenue, subject us to liability, damage our reputation and cause customers to become dissatisfied and fail to renew their subscriptions or demand credits, any of which could materially and adversely affect our business.

If we are unable to hire, retain and motivate qualified personnel, our business will suffer.

Our future success depends, in part, on our ability to continue to attract and retain highly skilled personnel. From time to time we have experienced difficulty in hiring and retaining employees who have appropriate qualifications, and we are continuing our efforts to meet our hiring goals. We believe that there is, and will continue to be, intense competition for highly skilled executive, technical, marketing and other personnel with experience in the locations where we maintain offices. We must provide competitive compensation packages and a high-quality work environment to hire, retain and motivate employees. If we are unable to retain and motivate our existing employees and attract qualified personnel to fill key positions, we may be unable to manage our business effectively, including the development, marketing and sale of our services, which could adversely affect our business, results of operations and financial condition. To the extent we hire personnel from competitors, we also may be subject to allegations that they have been improperly solicited or divulged proprietary or other confidential information.

Volatility in, or lack of performance of, our stock price may also affect our ability to attract and retain key personnel. Many of our key personnel are, or will soon be, vested in a substantial amount of shares of common stock or stock awards. Employees may be more likely to terminate their employment with us if the shares they own or the shares underlying their vested options have significantly appreciated in value relative to the original purchase prices of the shares or the exercise prices of the options, or, conversely, if the exercise prices of the options that they hold are significantly above the trading price of our common

stock. Additionally, if our stock price underperforms or the outlook for our stock is negative, we may not be able to attract qualified personnel to join our business. Candidates making employment decisions, particularly in high-technology industries, often consider the value and growth potential of any equity they may receive in connection with their employment. As a result, any significant decline in the market price of our common stock may adversely affect our ability to attract or retain highly skilled executive, technical, marketing and other personnel. If we are unable to retain and attract highly-skilled employees, our business, results of operations and financial condition could be adversely affected.

We have experienced losses in the past, and we may not achieve or sustain profitability in the future.

We generated net losses of $13.0 million, $5.9 million and $3.9 million in 2014, 2015 and 2016, respectively, and a net loss of $4.7 million in the nine months ended September 30, 2017. As of September 30, 2017, we had an accumulated deficit of $48.3 million. We will need to generate and sustain increased revenue levels in future periods in order to achieve or sustain profitability. We also expect our costs to increase in future periods, which could negatively affect our future operating results if our revenue does not increase commensurately. For example, we intend to continue to expend significant funds to develop and enhance our technical infrastructure, platform and services, expand our research and development efforts and selling and marketing operations, including through increased headcount, meet the increased compliance requirements associated with our transition to and operation as a public company, and expand into new markets. Our efforts to grow our business may be more costly than we expect, and we may not be able to increase our revenue enough to offset our higher operating expenses. We may incur significant losses in the future for a number of reasons, including the other risks described in this prospectus, and unforeseen expenses, difficulties, complications and delays and other unknown events. If we are unable to achieve or sustain profitability, our stock price may significantly decrease.

We may require additional financing in the future and may not be able to obtain such financing on favorable terms, if at all, which could slow or stop our ability to grow or otherwise harm our business.

We intend to continue to make investments to support our business growth and may require additional funds to respond to business challenges, including the need to develop new features or enhance our platform, improve our operating infrastructure or acquire complementary businesses and technologies. To date, we have financed our operations primarily through our operations, private placements of our equity securities and debt financing provided by financial institutions. We may not be able to obtain additional financing on terms favorable to us, if at all. We may need to engage in equity or debt financings to secure additional funds. If we raise additional equity financing, our stockholders may experience significant dilution of their ownership interests and the per share value of our common stock could decline. If we engage in debt financing, the holders of debt would have priority over the holders of our common stock, and we may be required to accept terms that restrict our ability to incur additional indebtedness and our ability to operate our business. We may also be required to take other actions that would otherwise be in the interests of the debt holders and force us to maintain specified liquidity or other ratios, any of which could harm our business, financial condition and operating results. If we are unable to obtain adequate financing or financing on terms satisfactory to us when we require it, our ability to continue to support our business growth and to respond to business challenges could be significantly impaired, and our business may be adversely affected.

Our future quarterly results may fluctuate significantly, and if we fail to meet the expectations of analysts or investors, our stock price and the value of your investment could decline substantially.

Our results of operations, including our revenue, operating expenses and cash flows have fluctuated from quarter to quarter in the past and may continue to fluctuate as a result of a variety of factors, many of which are outside of our control, may be difficult to predict and may or may not fully reflect the underlying performance of our business. Additionally, we have a limited operating history with the current scale of our

business, which makes it difficult to forecast our future results. Some of the factors that may cause our results of operations to fluctuate from quarter to quarter include:

The occurrence of one or more of the foregoing and other factors may cause our results of operations to vary significantly. Accordingly, our results of operations in any one quarter may not be meaningful and should not be relied upon as indicative of future performance. Additionally, if our quarterly results of operations fall below the expectations of investors or securities analysts who follow our stock, the price of our common stock could decline substantially, and we could face costly lawsuits, including securities class action suits.

Our revenue is directly correlated with the number of emails sent by our customers. During the fourth-quarter holiday season, our customers process a relatively higher number of transactions, run a greater number of marketing programs, and therefore send more emails. Partially because of this seasonality, a greater percentage of our annual revenue has come from our fourth quarter than from other quarters. In 2014, 2015 and 2016, 28% to 29% of our annual revenue was in our fourth quarter. While we believe that this seasonality has affected and will continue to affect our quarterly results, our rapid growth has largely masked seasonal trends to date. Seasonality may become more pronounced in the future to the extent our revenue mix shifts between our Email API, Marketing Campaigns and other revenue sources

over time. As a result, historical patterns in our business may not be a reliable indicator of our future performance.

Our reliance on cloud-based technologies from third parties may adversely affect our business, results of operations and financial condition.

We rely heavily on hosted cloud-based technologies from third parties in order to operate critical internal functions of our business, including our accounting, billing and office management functions. If these services become unavailable due to extended outages or interruptions, or because they are no longer available on commercially reasonable terms or prices, our expenses could increase. As a result, our ability to manage our operations could be interrupted and our processes for managing our sales process and supporting our customers could be impaired until equivalent services, if available, are identified, obtained and implemented, all of which could adversely affect our business, results of operations and financial condition.

Our corporate culture has contributed to our success, and if we cannot maintain this culture as we grow, we could lose the innovation, creativity and teamwork fostered by our culture, which could harm our business.

We believe that our culture has been and will continue to be a key contributor to our success. Between December 31, 2011 and September 30, 2017, we have increased the size of our full-time workforce by 350 employees, and we intend to continue to hire aggressively as we expand. If we do not continue to maintain our corporate culture as we grow, we may be unable to foster the innovation, creativity and teamwork we believe we need to support our growth. Moreover, many of our employees may be able to receive significant proceeds from sales of our common stock in the public markets after this offering, which could lead to disparities of wealth among our employees that adversely affects relations among employees and our culture in general. Our substantial anticipated headcount growth and our transition from a private company to a public company may result in a change to our corporate culture, which could harm our business.

Acquisition opportunities could be difficult to identify, and any pursued acquisitions could divert the attention of management, pose integration challenges, disrupt our business, dilute stockholder value and adversely affect our operating results and financial condition.

We have in the past acquired and may in the future seek to acquire or invest in businesses, products or technologies that we believe could complement or expand our platform, enhance our technical capabilities or otherwise offer growth opportunities. For example, in 2017, we acquired JCKM, Inc., or Bizzy, a marketing automation company. We do not know if we will be able to fully realize the anticipated benefits of this or other acquisitions and we may not be successful in integrating acquired technologies and businesses into our company. Acquisitions may disrupt our business, divert our resources and require significant management attention that would otherwise be available for development of our existing business.

We also may not achieve the anticipated benefits from an acquired business due to a number of factors, including:

In addition, a significant portion of the purchase price of companies we acquire may be allocated to goodwill and other intangible assets, which must be assessed for impairment at least annually. Acquisitions could also result in dilutive issuances of equity securities or the incurrence of debt, which could adversely affect our operating results. In the future, if our acquisitions do not yield expected returns, we may be required to take charges to our operating results based on this impairment assessment process, which could adversely affect our results of operations.

If the estimates and assumptions we have used to calculate the size of our total addressable target market are inaccurate, our future growth rate may be limited.

We have estimated the size of our total addressable target market based on data published by third parties and on internally generated data and assumptions. While we believe our market size information is generally reliable, such information is inherently imprecise, and relies on our and third parties' projections, assumptions and estimates within our target market, which are necessarily subject to a high degree of uncertainty and risk due to a variety of factors, including those described in this prospectus. If third-party or internally generated data prove to be inaccurate or we make errors in our assumptions based on that data, including how current customer data and trends may apply to potential future customers and the number and type of potential customers, our future growth rate may be lower than what we currently estimate. In addition, these inaccuracies or errors may cause us to misallocate capital and other business resources, which could divert resources from more valuable alternative projects and harm our business.

Even if our target market meets our size estimates, we may not grow our business. Our growth is subject to many factors, including our success in expanding our international operations, continuing to promote the use of our services by our customers for their marketing needs and otherwise implementing our business strategy, which are subject to many risks and uncertainties. Accordingly, the information regarding the size of our total addressable market included in this prospectus should not be taken as indicative of our future growth.

Our platform or services may infringe the intellectual property rights of third parties and this may create liability for us or otherwise harm our business.

From time to time third parties have claimed, and may in the future claim, that our platform capabilities or services infringe their intellectual property rights, and such claims may also result in claims against our customers. These claims may damage our brand and reputation, harm our customer relationships and create liability for us. We expect the number of such claims will increase as the number of

products and services and the level of competition in our market grows, the functionality of our platform or services overlap with that of other products and services, and the volume of issued software patents and patent applications continues to increase.

Companies in the software and technology industries, including some of our current and potential competitors, own large numbers of patents, copyrights, trademarks, and trade secrets and frequently enter into litigation based on allegations of infringement or other violations of intellectual property rights. In addition, many of these companies have the capability to dedicate substantially greater resources to enforce their intellectual property rights and to defend claims that may be brought against them. Furthermore, patent holding companies, non-practicing entities and other adverse patent owners that are not deterred by our existing intellectual property protections have asserted, and in the future may seek to assert, patent claims against us. From time to time, third parties have contacted us inviting us to license their patents and may, in the future, assert patent, copyright, trademark or other intellectual property rights against us, our strategic partners or our customers. We have received, and may in the future receive, notices that claim we have misappropriated, misused, or infringed other parties' intellectual property rights, and, to the extent we gain greater market visibility, we face a higher risk of being the subject of intellectual property infringement claims, which is not uncommon with respect to our market.

There may be third-party intellectual property rights, including issued or pending patents, that cover significant aspects of our technologies or business methods. In addition, if we acquire or license technologies from third parties, we may be exposed to increased risk of being the subject of intellectual property infringement due to, among other things, our lower level of visibility into the development process with respect to such technology and the care taken to safeguard against infringement risks. Any intellectual property claims, with or without merit, may be very time-consuming, may be expensive to settle or litigate, and may divert our management's attention and other resources. These claims may also subject us to significant liability for damages, potentially including treble damages if we are found to have willfully infringed patents or copyrights, and may require us to indemnify our customers for liabilities they incur as a result of such claims. These claims may also result in our having to stop using technology found to be in violation of a third party's rights. We may be required to seek a license for the intellectual property, which may not be available on reasonable terms or at all. Even if a license were available, we may be required to pay significant royalties, which would increase our operating expenses. Alternatively, we may be required to develop alternative non-infringing technology, which may require significant time, effort, and expense, and may affect the performance or features of our platform. If we cannot license or develop alternative non-infringing substitutes for any infringing technology used in any aspect of our business, we would be forced to limit or stop sales of our services and may be unable to compete effectively. Any of these results would adversely affect our business, operating results and financial condition.

Indemnity provisions in various agreements potentially expose us to substantial liability for intellectual property infringement and other losses.

Our agreements with customers and other third parties typically include indemnification or other provisions under which we agree to indemnify or otherwise be liable to them for losses suffered or incurred as a result of claims of intellectual property infringement or other liabilities relating to or arising from our platform or services or other acts or omissions. Large indemnity payments or damage claims from contractual breach could harm our business, results of operations and financial condition. Although we normally contractually limit our liability with respect to such obligations, we may still incur substantial liability related to them. Any dispute with a customer with respect to such obligations could have adverse effects on our relationship with that customer and other current and prospective customers, reduce demand for our platform and adversely affect our business, results of operations and financial condition.

Our platform contains third-party open source software components, and failure to comply with the terms of the underlying open source software licenses could restrict our ability to sell our services.

Our platform incorporates open source software code. An open source license allows the use, modification and distribution of software in source code form. Certain kinds of open source licenses further require that any person who creates a product or service that contains, links to, or is derived from software that was subject to an open source license must also make their own product or service subject to the same open source license. Using software that is subject to this kind of open source license can lead to a requirement that our services be provided free of charge or be made available or distributed in source code form. Although we do not believe our platform includes any open source software in a manner that would result in the imposition of any such requirement, the interpretation of open source licenses is legally complex and, despite our efforts, it is possible that our platform could be found to contain this type of open source software. Further, few of the licenses applicable to open source software have been interpreted by courts, and there is a risk that these licenses could be construed in a manner that could impose unanticipated conditions or restrictions on our ability to commercialize our platform or services in the future.

Moreover, we cannot assure you that our processes for controlling our use of open source software in our platform will be effective. If we have not complied with the terms of an applicable open source software license, we could be required to seek licenses from third parties to continue offering our platform on terms that are not economically feasible, to re-engineer our services to remove or replace the open source software, to discontinue the sale of our services if re-engineering could not be accomplished on a timely basis, to pay monetary damages, or to make generally available the source code for our proprietary technology, any of which could adversely affect our business, operating results, and financial condition.

In addition to risks related to license requirements, use of open source software can involve greater risks than those associated with use of third-party commercial software, as open source licensors generally do not provide warranties or assurance of title, performance, non-infringement, or controls on origin of the software. There is typically no support available for open source software, and we cannot assure you that the authors of such open source software will not abandon further development and maintenance. Many of the risks associated with the use of open source software, such as the lack of warranties or assurances of title or performance, cannot be eliminated, and could, if not properly addressed, negatively affect our business. We have established processes to help alleviate these risks, including a review process for screening requests from our development organizations for the use of open source software, but we cannot be sure that all open source software is identified or submitted for approval prior to use in our platform.

Responding to any infringement claim, regardless of its validity, or discovering open source software code in our platform could harm our business, operating results and financial condition, by, among other things:

Any failure to protect our proprietary technology and intellectual property rights could substantially harm our business and operating results.

Our success and ability to compete depend in part on our ability to protect our proprietary technology and intellectual property. To safeguard these rights, we rely on a combination of patent, trademark, copyright and trade secret laws and contractual protections in the United States and other jurisdictions, all of which provide only limited protection and may not now or in the future provide us with a competitive advantage.

In order to protect our unpatented proprietary technologies and processes, we rely on trade secret laws and confidentiality and invention assignment agreements with our employees, consultants, strategic partners, vendors and others. Also, despite our efforts to protect our proprietary technology and trade secrets, unauthorized parties may attempt to misappropriate, copy, reverse engineer or otherwise obtain and use them. In addition, others may independently discover our trade secrets, in which case we would not be able to assert trade secret rights, or develop similar technologies and processes. Further, the contractual provisions that we enter into may not prevent unauthorized use or disclosure of our proprietary technology or intellectual property rights and may not provide an adequate remedy in the event of unauthorized use or disclosure of our proprietary technology or intellectual property rights. Moreover, policing unauthorized use of our technologies, trade secrets and intellectual property is difficult, expensive and time-consuming, particularly in foreign countries where the laws may not be as protective of intellectual property rights as those in the United States and where mechanisms for enforcement of intellectual property rights may be weak. To the extent that we expand our activities outside of the United States, our exposure to unauthorized copying and use of our platform and proprietary information may increase. We may be unable to determine the extent of any unauthorized use or infringement of our platform, technologies or intellectual property rights.

We cannot assure you that any patents we have obtained or that may issue to us in the future will give us the protection that we seek or that such patents will not be challenged, invalidated or circumvented. As of September 30, 2017, we had one issued patent. Any patents that may issue to us in the future may not provide sufficiently broad protection and may not be enforceable in actions against alleged infringers. Obtaining and enforcing software patents in the United States is becoming increasingly challenging. Any patents we have obtained or may obtain in the future may be found to be invalid or unenforceable in light of recent and future changes in the law. Similarly, we cannot assure you that any future trademark registrations will be issued from current or future applications or that any registered trademarks we have obtained or may obtain in the future will be enforceable or provide adequate protection of our proprietary rights. We also license software from third parties for integration into our software, including open source software and other software available on commercially reasonable terms. We cannot assure you that such third parties will maintain such software or continue to make it available.

There can be no assurance that the steps that we take will be adequate to protect our proprietary technology and intellectual property, that others will not develop or patent similar or superior technologies, products or services, or that our trademark, patent and other intellectual property rights will not be challenged, invalidated or circumvented by others. Furthermore, effective trademark, patent, copyright and trade secret protection may not be available in every country in which our software is available or where we have employees or independent contractors. In addition, the legal standards relating to the validity, enforceability, and scope of protection of intellectual property rights in internet and software-related industries are uncertain and still evolving.

In order to protect our proprietary technology and intellectual property rights, we may be required to spend significant resources to monitor and protect these rights. Litigation brought to protect and enforce our intellectual property rights could be costly, time-consuming and distracting to management and could result in the impairment or loss of portions of our intellectual property. Furthermore, our efforts to enforce our proprietary technology and intellectual property rights may be met with defenses,

counterclaims and countersuits attacking the validity and enforceability of our intellectual property rights. Our failure to secure, protect and enforce our intellectual property rights could materially and adversely affect our business.

We face exposure to foreign currency exchange rate fluctuations, and such fluctuations could adversely affect our business, results of operations and financial condition.

As our international operations expand beyond our current London location, our exposure to the effects of fluctuations in currency exchange rates grows. While we have primarily transacted with customers and business partners in U.S. dollars, we expect to expand the number of transactions with customers and business partners that are denominated in foreign currencies in the future as we expand our business internationally. We incur expenses for some of our internet service provider costs outside of the United States in local currencies and for employee compensation and other operating expenses at our U.K. location in British pounds. Fluctuations in the exchange rates between the U.S. dollar and other currencies could result in an increase to the U.S. dollar equivalent of such expenses.

Accordingly, changes in the value of foreign currencies relative to the U.S. dollar may, particularly in the future as we expand our business internationally, affect our results of operations due to transactional and translational remeasurements. As a result of such foreign currency exchange rate fluctuations, it could be more difficult to detect underlying trends in our business and results of operations. In addition, to the extent that fluctuations in currency exchange rates cause our results of operations to differ from our expectations or the expectations of our investors and securities analysts who follow our stock, the trading price of our common stock could be adversely affected.

Our subscription agreements are denominated in U.S. dollars, and therefore our revenue currently is not subject to foreign currency risk. However, a strengthening of the U.S. dollar could increase the real cost of our platform to current and prospective customers outside of the United States, adversely affecting our business, results of operations and financial condition.

We do not currently maintain a program to hedge transactional exposures in foreign currencies. However, in the future, we may use derivative instruments, such as foreign currency forward and option contracts, to hedge certain exposures to fluctuations in foreign currency exchange rates. The use of such hedging activities may not offset any or more than a portion of the adverse financial effects of unfavorable movements in foreign exchange rates over the limited time the hedges are in place. Moreover, the use of hedging instruments may introduce additional risks if we are unable to structure effective hedges with such instruments.

Taxing authorities may successfully assert that we should have collected or paid, or in the future should collect or pay, sales, use, value added or similar taxes, and we could be subject to liability with respect to past or future sales, which could adversely affect our financial results.

We do not collect sales, use, value added and similar taxes in all jurisdictions in which we have sales, based on our belief that such taxes are not applicable. Sales, use, value added and similar tax laws and rates vary greatly by jurisdiction. Certain jurisdictions in which we do not collect such taxes may assert that such taxes are applicable, which could result in tax assessments, penalties and interest, and we may be required to collect and/or remit such taxes in the future. While we reserve estimated amounts with respect to such taxes on our financial statements, we cannot be certain that we have made sufficient reserves to cover such tax liabilities or such taxes. If our reserve amounts are inadequate, such tax assessments, penalties and interest or future requirements may adversely affect our results of operations and financial condition. Additionally, the application of federal, state, local and international tax laws to cloud services are continuously evolving. Income, sales, use or other tax laws, statutes, rules, regulations or ordinances could be enacted or amended at any time, possibly with retroactive effect, which could increase our taxes and ultimately have a negative impact on our results of operations and cash flows.

Our ability to use our net operating losses to offset future taxable income may be subject to certain limitations.

As of December 31, 2016, we had net operating loss, or NOL, carryforwards for U.S. federal income tax purposes of approximately $33.9 million, which expire in various years beginning in 2029 if not utilized. In general, under Section 382 of the United States Internal Revenue Code of 1986, as amended, or the Code, a corporation that undergoes an "ownership change" is subject to limitations on its ability to utilize its pre-ownership change NOLs to offset future taxable income. We are currently in the process of completing a study under Section 382 of the Code to determine the impact that ownership changes during and prior to the year ended December 31, 2016, if any, may have had on our NOLs and expect to complete the analysis within the next twelve months. As a result of this analysis, we may have an adjustment in our available NOLs recorded at December 31, 2016. If our existing NOLs are subject to limitations arising from previous ownership changes, or if we undergo an ownership change in connection with or after this offering, our ability to utilize pre-change NOLs could be further limited by Section 382. Future changes in our stock ownership, some of which are outside of our control, could also result in an ownership change under Section 382 of the Code. We will be unable to use our NOLs if we do not attain profitability sufficient to offset such available NOLs prior to their expiration. Furthermore, our ability to utilize NOLs of companies that we may acquire in the future may be subject to limitations. There is also a risk that due to regulatory changes, such as suspensions on the use of NOLs, or other unforeseen reasons, our existing NOLs could expire or otherwise be unavailable to offset future taxable income. For these reasons, we may not be able to utilize a portion of the NOLs reflected on our balance sheet, even if we attain profitability.

The enactment of legislation implementing changes in U.S. taxation of international business activities or the adoption of other tax reform policies could materially impact our financial condition and results of operations.

U.S. tax laws, including limitations on the ability of taxpayers to claim and utilize foreign tax credits and the deferral of certain tax deductions until earnings outside of the United States are repatriated to the United States, as well as changes to U.S. tax laws that may be enacted in the future, could impact the tax treatment of our foreign earnings. Due to the anticipated expansion of our international business activities, any changes in the U.S. taxation of such activities may increase our worldwide effective tax rate and adversely affect our financial condition and results of operations.

We are subject to federal, state and local taxes in the United States and the United Kingdom. Significant judgment is required in evaluating our tax positions and our worldwide provision for taxes. During the ordinary course of business, there are many activities and transactions for which the ultimate tax determination is uncertain. In addition, our tax obligations and effective tax rates could be adversely affected by changes in the relevant tax, accounting and other laws, regulations, principles and interpretations, including those relating to income tax nexus, by our earnings being lower than anticipated in jurisdictions where we have lower statutory rates and higher than anticipated in jurisdictions where we have higher statutory rates, by changes in foreign currency exchange rates, or by changes in the valuation of our deferred tax assets and liabilities. We may be audited in various jurisdictions, and such jurisdictions may assess additional taxes against us. Although we believe our tax estimates are reasonable, the final determination of any tax audits or litigation could be materially different from our historical tax provisions and accruals, which could have a material adverse effect on our operating results or cash flows in the period or periods for which a determination is made.

Unfavorable conditions in our industry or the global economy or reductions in marketing information technology spending could limit our ability to grow our business and negatively affect our results of operations.

Our results of operations may vary based on the impact of changes in our industry or the global economy on us or our customers. The revenue growth and potential profitability of our business depend on demand for email services and email marketing generally and for our services in particular. Current or

future economic uncertainties or downturns could adversely affect our business and results of operations. Negative conditions in the general economy both in the United States and abroad, including conditions resulting from changes in gross domestic product growth, financial and credit market fluctuations, political turmoil, natural catastrophes, warfare and terrorist attacks on the United States, Europe, the Asia Pacific region or elsewhere, could cause a decrease in business investments, including spending on information technology, and negatively affect the growth of our business. To the extent our platform or services are perceived by customers and potential customers as discretionary, there may be delays or reductions in spending on our services, we may need to reduce our prices in order to remain competitive and our revenue may decline. In addition, the increased pace of consolidation in certain industries may result in reduced overall spending on our platform and services. We cannot predict the timing, magnitude or duration of any economic slowdown, instability or recovery, generally or within any particular industry. If the economic conditions of the general economy or markets in which we operate worsen, our business, results of operations and financial condition could be adversely affected.

Furthermore, many of our customers are SMBs. These organizations frequently have limited budgets and are often resource- and time-constrained and, as a result, may be significantly more affected by economic downturns than their larger, more established counterparts. As a result, SMBs may choose to spend the limited funds that they have on items other than our services. Moreover, if SMBs experience economic distress, they may be unwilling or unable to expend time and financial resources on email, which could negatively affect the overall demand for our platform, increase customer attrition and cause our revenue growth or operating results to decline.

The success of our business depends on the continued growth and acceptance of email as a communications tool and the related accessibility, expansion and reliability of the Internet infrastructure.

The future success of our business depends on the continued widespread use of email as a primary means of communication and as the document of record for many digital business transactions. Security problems such as viruses, worms and other malicious programs, reliability issues arising from outages and damage to the Internet infrastructure or an overabundance of spam could create the perception that email is not a safe, reliable or efficient means of communication, which would discourage businesses and consumers from using email. In addition, alternative communications tools such as social media or text messaging have gained significant widespread acceptance and may gain additional acceptance for both email marketing and transactional record purposes. To the extent use of these alternative communications tools continues to grow, these tools could be used by our customers as a substitute for our services, and demand for our services and our revenues could decline.

Furthermore, federal, state or foreign government bodies or agencies have in the past adopted, and may in the future adopt, laws or regulations affecting the use of the Internet as a commercial medium. In addition, government agencies or private organizations have imposed and may impose additional taxes, fees or other charges for accessing the Internet or commerce conducted via the Internet. We provide our platform through the Internet and many of our customers use our services in connection with their own online transactions. Changes in these laws or regulations could require us to modify our platform in order to comply with these changes and could impact our customers' businesses, reducing demand for our services. These laws or charges could limit the growth of Internet-related commerce or the use of Internet communications such as email, or result in reductions in the demand for Internet-based services such as our platform. In addition, the use of the Internet and email as business tools could be adversely affected due to delays in the development or adoption of new standards and protocols to handle increased demands in Internet activity, security, reliability, cost, ease-of-use, accessibility and quality of service. Any decrease in the use of the Internet or email would reduce demand for our platform and harm our business.

If we experience excessive credit card or other fraudulent activity, we could incur substantial costs.

Most of our customers authorize us to bill their credit card or other online accounts directly for subscription fees that we charge. If people pay for our services with stolen credit cards or other wrongly obtained online account information, we could incur substantial third-party vendor costs for which we may not be reimbursed. Further, our customers provide us with credit card billing information online, and we do not review the physical credit cards used in these transactions, which increases our risk of exposure to fraudulent activity. We also incur charges, which we refer to as chargebacks, from the credit card and other online payment processing companies from claims that the customer did not authorize the credit card or other online transaction to purchase our subscription. If the number of unauthorized credit card or other online transactions becomes excessive, we could be assessed substantial fines for excess chargebacks and we could lose the right to accept credit cards or other online accounts for payment, which could have a material adverse effect on our business and operating results.

Our reported financial results may be adversely affected by changes in accounting principles generally accepted in the United States.

Generally accepted accounting principles in the United States, or GAAP, are subject to interpretation by the Financial Accounting Standards Board, or the FASB, the Securities and Exchange Commission, or the SEC, and various bodies formed to promulgate and interpret appropriate accounting principles. A change in these principles or interpretations could have a significant effect on our reported financial results for periods prior to and subsequent to such change, and could affect the reporting of transactions completed before the announcement of a change.

In particular, in May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606), which supersedes the revenue recognition requirements in ASC 605, Revenue Recognition. The core principle of ASU 2014-09 is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services; this new accounting standard also impacts the recognition of sales commissions. As an "emerging growth company" the JOBS Act allows us to delay adoption of new or revised accounting pronouncements applicable to public companies until such pronouncements are made applicable to private companies. We have elected to use this extended transition period under the JOBS Act with respect to ASU 2014-09, and as a result ASU 2014-09 will become applicable to us on January 1, 2019.

ASU 2014-09 permits the use of either a retrospective or cumulative effect transition method. We continue to evaluate the impact of the new standard and available adoption methods on our consolidated financial statements. We are in the process of evaluating arrangements with customers and identifying differences in accounting between new and existing standards. Regardless of the transition method, the application of this new guidance could have an adverse effect on our operating results in one or more periods as compared to what they would have been under current standards.

If our estimates or judgments relating to our critical accounting policies prove to be incorrect, our results of operations could be adversely affected.

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. We base our estimates on historical experience and on various other assumptions that we believe to be reasonable under the circumstances, as provided in the section titled "Management's Discussion and Analysis of Financial Condition and Results of Operations." The results of these estimates form the basis for making judgments about the carrying values of assets, liabilities and equity, and the amount of revenue and expenses that are not readily apparent from other sources. Significant assumptions and estimates used in preparing our consolidated financial statements include those related to revenue

recognition, valuation of goodwill and intangible assets, and stock-based compensation. Our results of operations may be adversely affected if our assumptions change or if actual circumstances differ from those in our assumptions, which could cause our results of operations to fall below the expectations of securities analysts and investors, resulting in a decline in the trading price of our common stock.

The requirements of being a public company may strain our resources, divert management's attention and affect our ability to attract and retain executive management and qualified board members.

As a public company, we will be subject to the reporting requirements of the Securities Exchange Act of 1934, as amended, or the Exchange Act, the Sarbanes-Oxley Act of 2002, or the Sarbanes-Oxley Act, the Dodd-Frank Wall Street Reform and Consumer Protection Act, the listing requirements of the New York Stock Exchange and other applicable securities rules and regulations. Compliance with these rules and regulations will increase our legal and financial compliance costs, make some activities more difficult, time-consuming or costly, and increase demand on our systems and resources, particularly after we are no longer an "emerging growth company" as defined in the JOBS Act.

In addition, changing laws, regulations and standards relating to corporate governance and public disclosure are creating uncertainty for public companies, further increasing legal and financial compliance costs, and making some activities more time consuming. These laws, regulations and standards are subject to varying interpretations, in many cases due to their lack of specificity, and, as a result, their application in practice may evolve over time as new guidance is provided by regulatory and governing bodies. This could result in continuing uncertainty regarding compliance matters and higher costs necessitated by ongoing revisions to disclosure and governance practices. We intend to invest substantial resources to comply with evolving laws, regulations and standards, and this investment may result in increased general and administrative expense and a diversion of management's time and attention from revenue-generating activities to compliance activities. If our efforts to comply with new laws, regulations and standards differ from the activities intended by regulatory or governing bodies due to ambiguities related to their application and practice, regulatory authorities may initiate legal proceedings against us and our business may be adversely affected.

Moreover, the demands on management in operating a publicly-traded company, interacting with public company investors and complying with the increasingly complex laws pertaining to public companies, are significant. Our management team may not successfully or efficiently manage us as a public company subject to significant regulatory oversight and reporting obligations under the federal securities laws and the continuous scrutiny of securities analysts and investors. These new obligations and constituents require significant attention from our senior management and could divert their attention away from the day-to-day management of our business, which could adversely affect our business, results of operations and financial condition.

We also expect that being a public company will make it more expensive for us to obtain director and officer liability insurance, and we may be required to accept reduced coverage or incur substantially higher costs to obtain coverage. These factors could also make it more difficult for us to attract and retain qualified members of our board of directors and qualified executive officers.

If we are unable to implement and maintain effective internal controls over financial reporting in the future, investors may lose confidence in the accuracy and completeness of our financial reports and the market price of our common stock may be negatively affected.

As a public company, we will be required to maintain internal controls over financial reporting and to report any material weaknesses in such internal controls. Section 404 of the Sarbanes-Oxley Act requires that we furnish a report by management on, among other things, the effectiveness of our internal control over financial reporting for the year ending December 31, 2018. This assessment will need to include disclosure of any material weaknesses identified by our management in our internal control over financial

reporting, as well as a statement that our independent registered public accounting firm has issued an opinion on our internal control over financial reporting, provided that our independent registered public accounting firm will not be required to attest to the effectiveness of our internal control over financial reporting until our first annual report required to be filed with the SEC following the date we are no longer an "emerging growth company," as defined in the JOBS Act.

If we have a material weakness in our internal controls over financial reporting, we may not detect errors on a timely basis and our financial statements may be materially misstated. We are in the process of designing and implementing the internal controls over financial reporting required to comply with this obligation, which process will be time-consuming, costly and complicated. If we identify material weaknesses in our internal controls over financial reporting, if we are unable to comply with the requirements of Section 404 in a timely manner, if we are unable to assert that our internal controls over financial reporting are effective, or if our independent registered public accounting firm is unable to express an opinion as to the effectiveness of our internal controls over financial reporting, when required, investors may lose confidence in the accuracy and completeness of our financial reports, and the market price of our common stock could be negatively affected. In addition, we could become subject to investigations by the New York Stock Exchange, the SEC or other regulatory authorities, which could require additional financial and management resources and adversely affect our business, financial condition and operating results.

There has been no prior market for our common stock. An active market may not develop or be sustained and investors may not be able to resell their shares at or above the initial public offering price.

There has been no public market for our common stock prior to this offering. The initial public offering price for our common stock will be determined through negotiations between the underwriters and us and may vary from the market price of our common stock following this offering. If you purchase shares of our common stock in this offering, you may not be able to resell those shares at or above the initial public offering price, if at all.

Our common stock has been approved for listing on the New York Stock Exchange under the symbol "SEND." However, there can be no assurance that an active trading market for our common stock will develop on that exchange or elsewhere or, if developed, that any market will be sustained. The lack of an active trading market for our common stock could depress the market price of our common stock and could affect your ability to sell your shares, thus causing the value of any investment in our common stock to decline.

Our stock price may be volatile, and the value of any investment in our common stock may decline.

The trading price of our common stock following this offering is likely to be highly volatile and could be subject to wide fluctuations in response to various factors, many of which are beyond our control. In addition to the factors discussed in this "Risk Factors" section and elsewhere in this prospectus, these factors include:

In addition, the stock market in general, and the market for technology companies in particular, has experienced extreme price and volume fluctuations that have often been unrelated or disproportionate to the operating performance of those companies. Broad market and industry factors may seriously affect the market price of our stock regardless of actual operating performance. These fluctuations may be even more pronounced in the trading market for our stock shortly following this offering. Securities class action litigation has often been instituted against companies following periods of volatility in the market price of their securities. This form of litigation, if instituted against us, could result in very substantial costs, divert our management's attention and resources and harm our business, operating results and financial condition.

As a new investor, you will experience immediate and substantial dilution in the book value of the shares that you purchase in this offering.

The initial public offering price is substantially higher than the pro forma net tangible book value per share of our common stock immediately following this offering based on the total value of our tangible assets less our total liabilities. Therefore, if you purchase shares of our common stock in this offering, at the assumed initial public offering price of $14.50 per share, which is the midpoint of the estimated offering price range set forth on the cover page of this prospectus, you will experience immediate dilution of $11.05 per share, the difference between the price per share you pay for our common stock and our pro forma net tangible book value per share as of September 30, 2017, after giving effect to the issuance of 7,700,000 shares of our common stock in this offering. See "Dilution." To the extent outstanding options or warrants to purchase our common stock are exercised, investors purchasing our common stock in this offering will experience further dilution.

Substantial future sales of shares of our common stock could cause the market price of our common stock to decline.

The market price of our common stock could decline as a result of substantial sales of our common stock, particularly sales by our directors, executive officers and significant stockholders, a large number of shares of our common stock becoming available for sale or the perception in the market that holders of a large number of shares intend to sell their shares. After this offering, there will be 40,291,661 shares of our common stock outstanding, based on the number of shares outstanding as of September 30, 2017, including the shares to be sold in this offering, which may be resold in the public market immediately. Substantially all of the remaining shares are currently restricted as a result of market stand-off agreements restricting their sale during the period ending 180 days after the date of this prospectus. In addition, substantially all of these shares are also subject to lock-up agreements with the representatives of the underwriters. Morgan Stanley & Co. LLC on behalf of the underwriters may, in its sole discretion, permit our officers, directors,

employees and current security holders who are subject to lock-up agreements to sell shares prior to the expiration of the lock-up agreements.

Additionally, 12,204,455 shares of our common stock subject to outstanding options and awards under our equity incentive plans as of September 30, 2017, will become eligible for sale in the public market in the future, subject to applicable vesting requirements, the lock-up agreements and market standoff provisions described above and Rules 144 and 701 under the Securities Act. See "Shares Eligible for Future Sale" for a more detailed description of sales that may occur in the future.

We also intend to register all shares of our common stock that will be reserved for issuance under our 2017 Equity Incentive Plan and our 2017 ESPP. Once we register these shares, they can be freely sold in the public market upon issuance and once vested and exercised, as applicable, subject to the lock-up agreements described above.

As of September 30, 2017, the holders of an aggregate of 24,471,780 shares of our convertible preferred stock, which shares of convertible preferred stock will be converted into 24,471,780 shares of our common stock upon the closing of this offering, have rights, subject to certain conditions, to require us to file registration statements covering their shares and to include their shares in registration statements that we may file for ourselves or other stockholders. The holder of the warrant to purchase 54,269 shares of our convertible preferred stock, which warrant will convert into a warrant to purchase 54,269 shares of our common stock upon the closing of this offering, also has these registration rights. The stockholders with these registration rights have waived such rights with respect to this offering.

We may issue shares of our common stock or securities convertible into our common stock from time to time in connection with a financing, acquisition, investment or otherwise. Any such issuance could result in substantial dilution to our existing stockholders and cause the trading price of our common stock to decline.

Our management will have broad discretion over the use of the proceeds we receive in this offering and might not apply the proceeds in ways that increase the value of your investment.

Our management generally will have broad discretion to use the net proceeds to us from this offering, and you will be relying on the judgment of our management regarding the application of these proceeds. Our management might not apply the net proceeds from this offering in ways that increase the value of your investment. We intend to use the net proceeds to us from this offering for working capital and other general corporate purposes, including developing and enhancing our technical infrastructure, platform and services, expanding our research and development efforts and selling and marketing operations, meeting the increased compliance requirements associated with our transition to and operation as a public company, and expanding into new markets. We may also use a portion to make acquisitions or investments. However, we do not have any agreements or commitments for any acquisitions or strategic investments at this time. Until we use the net proceeds to us from this offering, we plan to invest them, and these investments may not yield a favorable rate of return. If we do not invest or apply the net proceeds from this offering in ways that enhance stockholder value, we may fail to achieve expected financial results, which could cause our stock price to decline.

Concentration of ownership among our officers, directors, significant stockholders and their affiliates may prevent new investors, including purchasers in this offering, from influencing corporate decisions.

Our officers, directors and their affiliated funds and each of our stockholders who own greater than 5% of our outstanding common stock and their affiliates, in the aggregate, will beneficially own an aggregate of approximately 66.5% of the outstanding shares of our common stock following this offering, assuming no exercise of the underwriters' option to purchase additional shares. If the existing stockholders associated with Bessemer Venture Partners, which is an affiliate of a member of our board of directors, purchase shares of our common stock with an aggregate price of $10.0 million in this offering (the

maximum indicated interest, as described above), assuming no exercise of the underwriters' option to purchase additional shares, our officers, directors and their affiliated funds and each of our stockholders who own greater than 5% of our outstanding common stock and their affiliates, in the aggregate, will beneficially own an aggregate of approximately 68.1% of our outstanding common stock following this offering, assuming an initial public offering price of $14.50 per share, which is the midpoint of the estimated offering price range set forth on the cover page of this prospectus. As a result, if some of these persons or entities act together, they will have significant influence over the outcome of matters submitted to our stockholders for approval, including the election of directors and approval of significant corporate transactions, such as a merger or other sale of our company or our assets. This concentration of ownership could limit the ability of other stockholders to influence corporate matters and may have the effect of delaying or preventing a change of control of our company. Some of these persons or entities may have interests different from yours. For example, because many of these stockholders purchased their shares at prices substantially below the price at which shares are being sold in this offering and have held their shares for a relatively longer period, they may be more interested in selling the company to an acquirer than other investors.

We never have declared or paid any cash dividends on our capital stock and do not intend to pay any cash dividends in the foreseeable future. In addition, our credit facility restricts, and any future debt or preferred security arrangements may restrict, our ability to make distributions to our stockholders. We anticipate that we will retain any future earnings for use in the development of our business and for general corporate purposes. Any determination to pay dividends in the future will be at the discretion of our board of directors. Accordingly, investors must rely on sales of their shares of our common stock after price appreciation, which may never occur, as the only way to realize any future gains on their investments.

We are an "emerging growth company," and we cannot be certain if the reduced disclosure requirements applicable to emerging growth companies will make our common stock less attractive to investors.

For so long as we remain an "emerging growth company," as defined in the JOBS Act, we may take advantage of certain exemptions from various requirements that are applicable to public companies that are not "emerging growth companies," including not being required to comply with the independent auditor attestation requirements of Section 404 of the Sarbanes-Oxley Act, reduced disclosure obligations regarding executive compensation in our periodic reports and proxy statements, and exemptions from the requirements of holding a nonbinding advisory vote on executive compensation and stockholder approval of any golden parachute payments not previously approved. Further, we have elected to take advantage of the extended transition period to comply with new or revised accounting standards. As a result of the accounting standards election, we will not be subject to the same implementation timing for new or revised accounting standards as other public companies that are not emerging growth companies, which may make comparison of our financials to those of other public companies more difficult. We will remain an "emerging growth company" until the earliest of (i) the last day of the year following the fifth anniversary of the completion of our initial public offering, (ii) the last day of the first year in which our annual gross revenue is $1.07 billion or more, (iii) the date on which we have, during the previous rolling three-year period, issued more than $1.00 billion in non-convertible debt securities or (iv) the date on which we are deemed to be a "large accelerated filer" as defined in the Exchange Act. We cannot predict if investors will find our common stock less attractive because we may rely on these exemptions. If some investors find our common stock less attractive as a result, there may be a less active trading market for our common stock, and our stock price may be more volatile and may decline

Anti-takeover provisions in our charter documents and under Delaware law could make an acquisition of our company more difficult, limit attempts by our stockholders to replace or remove our current management and limit the market price of our common stock.

Provisions in our amended and restated certificate of incorporation and amended and restated bylaws to be effective in connection with the closing of this offering, may have the effect of delaying or preventing a change of control or changes in our management. Our amended and restated certificate of incorporation and amended and restated bylaws include provisions that:

These provisions may frustrate or prevent any attempts by our stockholders to replace or remove our current management by making it more difficult for stockholders to replace members of our board of directors, which is responsible for appointing the members of our management. In addition, because we are incorporated in Delaware, we are governed by the provisions of Section 203 of the Delaware General Corporation Law, which generally prohibits a Delaware corporation from engaging in any of a broad range of business combinations with any "interested" stockholder for a period of three years following the date on which the stockholder became an "interested" stockholder. Any delay or prevention of a change of control transaction or changes in our management could cause the market price of our common stock to decline.

Our amended and restated certificate of incorporation to be effective in connection with the closing of this offering will provide that the Court of Chancery of the State of Delaware or the U.S. federal district courts will be the exclusive forums for substantially all disputes between us and our stockholders, which could limit our stockholders' ability to obtain a favorable judicial forum for disputes with us or our directors, officers or other employees.

Our amended and restated certificate of incorporation to be effective in connection with the closing of this offering provides that the Court of Chancery of the State of Delaware is the sole and exclusive forum for any derivative action or proceeding brought on our behalf, any action asserting a breach of fiduciary duty owed by any of our directors, officers or other employees to us or our stockholders, any action asserting a claim against us arising pursuant to any provisions of the Delaware General Corporation Law,

our amended and restated certificate of incorporation or our amended and restated bylaws, or any action asserting a claim against us that is governed by the internal affairs doctrine. Our amended and restated certificate of incorporation further provides that the U.S. federal district courts will be the exclusive forum for resolving any complaint asserting a cause of action arising under the Securities Act. These choice of forum provisions may limit a stockholder's ability to bring a claim in a judicial forum that it finds favorable for disputes with us or our directors, officers or other employees, which may discourage such lawsuits. If a court were to find either choice of forum provision contained in our amended and restated certificate of incorporation to be inapplicable or unenforceable in an action, we may incur additional costs associated with resolving such action in other jurisdictions, which could adversely affect our results of operations and financial condition.

If securities or industry analysts do not publish research or publish inaccurate or unfavorable research about our business, our stock price and trading volume could decline.

The trading market for our common stock will depend in part on the research and reports that securities or industry analysts publish about us or our business. If too few securities analysts commence coverage of us, the trading price for our common stock would be negatively affected. If one or more of the analysts who cover us downgrade our common stock or publish inaccurate or unfavorable research about our business, our common stock price would likely decline. If one or more of these analysts cease coverage of us or fail to publish reports on us regularly, demand for our common stock could decrease, which might cause our common stock price and trading volume to decline.

Participation in this offering by certain of our existing stockholders would reduce the public float for our shares.

Certain of our existing stockholders associated with Bessemer Venture Partners, which is an affiliate of a member of our board of directors, have indicated an interest in purchasing shares of common stock with an aggregate price of up to $10.0 million in this offering. Because these indications of interest are not binding agreements or commitments to purchase, the underwriters may elect to sell fewer or no shares in this offering to such stockholders, or these stockholders may elect to purchase fewer or no shares in this offering. Assuming an initial public offering price of $14.50 per share, which is the midpoint of the estimated offering price range set forth on the cover page of this prospectus, if such stockholders were to purchase the entire $10.0 million of our common stock, they would purchase an aggregate of 689,655 shares of our common stock in this offering. If such stockholders purchase all such shares, assuming no exercise by the underwriters of their option to purchase additional shares, our officers, directors, and stockholders holding more than 5% of our capital stock as of September 30, 2017, and their affiliates, will beneficially own, in the aggregate, approximately 68.1% of our outstanding shares of common stock following this offering.

If these stockholders are allocated all or a portion of the shares in which they have indicated an interest in this offering and purchase any such shares, such purchase would reduce the available public float for our shares because such stockholders would be restricted from selling the shares by a lock-up agreement they have entered into with our underwriters (subject to certain exceptions) and by restrictions under applicable securities laws. As a result, any purchase of shares by such stockholders in this offering may reduce the liquidity of our common stock relative to what it would have been had these shares been purchased by investors that were not existing stockholders.

This prospectus, particularly in the sections titled "Prospectus Summary," "Risk Factors," "Management's Discussion and Analysis of Financial Condition and Results of Operations" and "Business," contains forward-looking statements that involve substantial risks and uncertainties. All statements other than statements of historical facts contained in this prospectus, including statements regarding our future financial condition, results of operations, business strategy and plans and objectives of management for future operations, as well as statements regarding industry trends, are forward-looking statements. In some cases, you can identify forward-looking statements by terminology such as "believe," "will," "may," "estimate," "continue," "anticipate," "intend," "should," "plan," "expect," "predict," "could," "potentially" or the negative of these terms or other similar expressions. We have based these forward-looking statements largely on our current expectations and projections about future events and trends that we believe may affect our financial condition, results of operations, business strategy and financial needs. These forward-looking statements are subject to a number of risks, uncertainties and assumptions described under the section titled "Risk Factors" and elsewhere in this prospectus, regarding, among other things:

These risks are not exhaustive. Other sections of this prospectus may include additional factors that could adversely impact our business and financial performance. New risk factors emerge from time to time and it is not possible for our management to predict all risk factors, nor can we assess the impact of all factors on our business or the extent to which any factor, or combination of factors, may cause actual results to differ materially from those contained in, or implied by, any forward-looking statements.

You should not rely upon forward-looking statements as predictions of future events. Although we believe that the expectations reflected in the forward-looking statements are reasonable, we cannot guarantee future results, levels of activity, performance or achievements. Except as required by law, we undertake no obligation to update publicly any forward-looking statements for any reason after the date of this prospectus.

You should read this prospectus and the documents that we have filed as exhibits to the registration statement on Form S-1, of which this prospectus is a part, that we have filed with the SEC with the understanding that our actual future results, levels of activity, performance and achievements may be materially different from what we expect.

Unless otherwise indicated, information contained in this prospectus concerning our industry and the market in which we operate, including our general expectations and market position, market opportunity and market size, is based on information from various sources, including data from the NAICS Association regarding the number of businesses with five or more employees, data from the Small Business Administration, or the SBA, regarding the percentage of businesses with a web presence and our own internal data on our average customer revenue, on assumptions that we have made that are based on that data and other similar sources, including the appropriateness and applicability of that data for our use, and on our knowledge of the markets for our services. This information involves a number of assumptions and limitations, and you are cautioned not to give undue weight to such estimates. While we believe the market position, market opportunity and market size information included in this prospectus is generally reliable, such information is inherently imprecise. In addition, projections, assumptions and estimates of our future performance and the future performance of the industry in which we operate is necessarily subject to a high degree of uncertainty and risk due to a variety of factors, including those described in the section titled "Risk Factors" and elsewhere in this prospectus. These and other factors could cause results to differ materially from those expressed in the estimates made by the independent parties and by us.

Certain information in the text of this prospectus is contained in independent industry publications. The sources of these independent industry publications are provided below:

We estimate that the net proceeds we will receive from this offering will be approximately $100.3 million, assuming an initial public offering price of $14.50 per share, which is the midpoint of the estimated offering price range set forth on the cover page of this prospectus, after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us.

Each $1.00 increase (decrease) in the assumed initial public offering price of $14.50 per share, which is the midpoint of the estimated offering price range set forth on the cover page of this prospectus, would increase (decrease) the net proceeds to us from this offering by approximately $7.2 million, assuming the number of shares offered by us, as set forth on the cover page of this prospectus, remains the same and after deducting the estimated underwriting discounts and commissions and estimated offering expenses payable by us. Similarly, each increase (decrease) of 1,000,000 shares in the number of shares of our common stock offered by us would increase (decrease) the net proceeds to us from this offering by approximately $13.5 million, assuming that the assumed initial public offering price of $14.50 per share remains the same, after deducting the estimated underwriting discounts and commissions and estimated offering expenses payable by us.

The principal purposes of this offering are to increase our capitalization and financial flexibility and create a public market for our common stock. Although we have not yet determined with certainty the manner in which we will allocate the net proceeds of this offering, we intend to use the net proceeds from this offering for working capital and other general corporate purposes, including developing and enhancing our technical infrastructure, platform and services, expanding our research and development efforts and selling and marketing operations, meeting the increased compliance requirements associated with our transition to and operation as a public company, and expanding into new markets.

We may also use a portion of the net proceeds to make acquisitions of or invest in businesses, products, services or technologies that we believe to be complementary. We do not have any agreements or commitments for any such acquisitions or investments at this time.

The expected use of net proceeds from this offering represents our intentions based upon our present plans and business conditions. We cannot predict with certainty all of the particular uses for the proceeds of this offering or the amounts that we will actually spend on the uses set forth above. Accordingly, we will have broad discretion in the application of the net proceeds, and investors will be relying on the judgment of our management regarding the application of the net proceeds of this offering. The timing and amount of capital expenditures will be based on many factors, including cash flows from operations and the anticipated growth of our business.

We have never declared or paid dividends on our capital stock. We currently intend to retain all available funds and any future earnings to support operations and to finance the growth and development of our business. We do not intend to declare or pay cash dividends on our common stock in the foreseeable future. The terms of our outstanding credit facility also restrict our ability to pay dividends, and we may also enter into credit agreements or other borrowing arrangements in the future that will restrict our ability to declare or pay cash dividends on our capital stock.

The following table sets forth our cash and cash equivalents and our capitalization as of September 30, 2017, on:

The pro forma as adjusted information below is illustrative only, and our capitalization following the completion of this offering will be adjusted based on the actual initial public offering price and other final terms of the offering.

You should read this table together with the sections of this prospectus titled "Summary Consolidated Financial Data," "Selected Consolidated Financial Data," "Description of Capital Stock" and "Management's Discussion and Analysis of Financial Condition and Results of Operations" and our audited consolidated financial statements and related notes included elsewhere in this prospectus.

	As of September 30, 2017

	Actual			Pro Forma			Pro Forma As Adjusted⁽¹⁾
	(unaudited)
	(in thousands, except share and per share data)
Cash and cash equivalents	$	37,397		$	37,397		$	137,682



Preferred stock warrant liability	$	635		$	—		$	—

Convertible preferred stock, par value $0.001 per share;
24,697,410 shares authorized, 24,535,227 issued and outstanding, actual; no shares authorized, issued, or outstanding, pro forma and pro forma as adjusted		80,688			—			—

Stockholders' equity (deficit):
Preferred stock, par value $0.001 per share; no shares authorized, issued or outstanding, actual; 10,000,000 shares authorized, no shares issued and outstanding, pro forma and pro forma as adjusted		—			—			—
Common stock, par value $0.001 per share, 50,000,000 shares authorized, 8,056,434 shares issued and outstanding, actual; 250,000,000 shares authorized, 32,591,661 shares issued and outstanding, pro forma; 250,000,000 shares authorized, 40,291,661 shares issued and outstanding, pro forma as adjusted		5			30			38
Additional paid-in-capital		9,330			90,628			190,905
Accumulated other comprehensive income (loss)		(3	)		(3	)		(3	)
Accumulated deficit		(48,331	)		(48,331	)		(48,331	)

Total stockholders' equity (deficit)		(38,999	)		43,324			142,609

Total capitalization	$	43,324		$	43,324		$	142,609

(1): Each $1.00 increase or decrease in the assumed initial public offering price of $14.50 per share, which is the midpoint of the estimated offering price range set forth on the cover page of this prospectus, would increase or decrease the pro forma as adjusted amount of each of cash and cash equivalents, additional paid-in capital, total stockholders' equity (deficit) and total capitalization by approximately $7.2 million, assuming that the number of shares offered by us, as set forth on the cover page of this prospectus, remains the same and after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us. Each increase or decrease of 1,000,000 in the number of shares we are offering would increase or decrease the pro forma as adjusted amount of each of cash and cash equivalents, additional paid-in capital, total stockholders' equity (deficit) and total capitalization by approximately $13.5 million, assuming that the assumed initial public offering price stays the same, after deducting the estimated underwriting discounts and commissions and estimated offering expenses payable by us.

The outstanding share information in the table above excludes, as of September 30, 2017, the following shares:

If you invest in our common stock in this offering, your ownership interest will be diluted immediately to the extent of the difference between the initial public offering price per share of our common stock and the pro forma as adjusted net tangible book value per share of our common stock immediately after this offering.

Net tangible book value per share is determined by dividing our total tangible assets less our total liabilities by the number of shares of our common stock outstanding. Our historical net tangible book value as of September 30, 2017, was $38.1 million, or $4.73 per share. Our pro forma net tangible book value as of September 30, 2017, was $38.8 million, or $1.19 per share, based on the total number of shares of our common stock outstanding as of September 30, 2017, after giving effect to (i) the automatic conversion of all outstanding shares of our convertible preferred stock as of September 30, 2017, into an aggregate of 24,535,227 shares of our common stock, which conversion will occur upon the closing of the offering and (ii) the reclassification of our preferred stock warrant liability to additional paid-in capital upon the closing of this offering.

After giving effect to the sale of shares of our common stock in this offering at the assumed initial public offering price of $14.50 per share, which is the midpoint of the estimated offering price range set forth on the cover page of this prospectus, and after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us, our pro forma as adjusted net tangible book value as of September 30, 2017, would have been $139.0 million, or $3.45 per share. This represents an immediate increase in pro forma net tangible book value of $2.26 per share to our existing stockholders and an immediate dilution in pro forma net tangible book value of $11.05 per share to investors purchasing shares of our common stock in this offering at the assumed initial public offering price.

The following table illustrates this dilution on a per share basis to new investors:

Each $1.00 increase or decrease in the assumed initial public offering price of $14.50 per share, which is the midpoint of the estimated offering price range set forth on the cover page of this prospectus, would increase or decrease, as applicable, our pro forma as adjusted net tangible book value per share to new investors by $0.18, and would increase or decrease, as applicable, dilution per share to new investors in this offering by $0.82, assuming that the number of shares offered by us, as set forth on the cover page of this prospectus, remains the same and after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us. Each increase or decrease of 1,000,000 shares in the number of shares of our common stock we are offering would increase or decrease the pro forma as adjusted net tangible book value by approximately $0.24 per share and the dilution to new investors by $(0.24) per share, assuming the assumed initial public offering price remains the same and after deducting the estimated underwriting discounts and commissions and estimated offering expenses payable by us.

If the underwriters exercise their over-allotment option in full, the pro forma as adjusted net tangible book value per share would be $3.73 per share, and the dilution in pro forma net tangible book value per share to new investors in this offering would be $10.77 per share.

Each $1.00 increase or decrease in the assumed initial public offering price of $14.50 per share, which is the midpoint of the estimated offering price range set forth on the cover page of this prospectus, would increase or decrease, as applicable, the total consideration paid by new investors and total consideration paid by all stockholders by approximately $7.7 million, assuming that the number of shares offered by us, as set forth on the cover page of this prospectus, remains the same and without deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us.

In addition, to the extent any outstanding options or the outstanding warrant are exercised, new investors would experience further dilution.

Except as otherwise indicated, the above discussion and tables assume no exercise of the underwriters' over-allotment option. If the underwriters exercise their over-allotment option in full, our existing stockholders would own 79% and our new investors would own 21% of the total number of shares of our common stock outstanding upon the closing of this offering.

The number of shares of our common stock that will be outstanding after this offering is based on 32,591,661 shares outstanding as of September 30, 2017, and excludes:

The following tables summarize our historical consolidated financial data. We have derived the historical consolidated statements of operations data for the years ended December 31, 2014, 2015 and 2016, and the consolidated balance sheet data as of December 31, 2015 and 2016, from our audited consolidated financial statements included elsewhere in this prospectus. We have derived the historical consolidated statements of operations data for the nine months ended September 30, 2016 and 2017, and the historical consolidated balance sheet data as of September 30, 2017, from our unaudited interim consolidated financial statements included elsewhere in this prospectus. In management's opinion, we have prepared our unaudited interim consolidated financial statements on the same basis as our audited consolidated financial statements and have included all adjustments, which include only normal recurring adjustments, necessary to state fairly the financial information set forth in those statements. The following summary consolidated financial data should be read in conjunction with the section titled "Management's Discussion and Analysis of Financial Condition and Results of Operations" and our consolidated financial statements and related notes included elsewhere in this prospectus. Our historical results are not necessarily indicative of the results that may be expected in the future and our results for the nine months ended September 30, 2017, are not necessarily indicative of the results that may be expected for the full year or any other period.

	For the Year Ended December 31,									For the Nine Months Ended September 30,

	2014			2015			2016			2016			2017
	(In thousands, except per share amounts)
Consolidated Statements of Operations Data:
Revenue	$	42,776		$	58,476		$	79,929		$	56,858		$	80,159
Cost of revenue⁽¹⁾⁽²⁾		15,187			18,961			21,605			15,995			21,357

Gross profit		27,589			39,515			58,324			40,863			58,802

Operating expenses:⁽¹⁾⁽²⁾
Research and development		15,290			18,959			21,178			15,632			21,208
Selling and marketing		15,260			13,737			21,800			15,311			20,582
General and administrative⁽³⁾⁽⁴⁾		9,550			12,477			18,920			13,091			21,222
Loss on disposal of assets		63			1			27			27			2

Total operating expenses		40,163			45,174			61,925			44,061			63,014

Loss from operations		(12,574	)		(5,659	)		(3,601	)		(3,198	)		(4,212	)
Other income (expense), net⁽⁵⁾		(386	)		(195	)		(307	)		(285	)		(515	)
Net loss before provision for income taxes		(12,960	)		(5,854	)		(3,908	)		(3,483	)		(4,727	)
Provision for income taxes		—			—			—			—			—

Net loss	$	(12,960	)	$	(5,854	)	$	(3,908	)	$	(3,483	)	$	(4,727	)



Weighted average shares used in computing net loss per share, basic and diluted⁽⁶⁾		5,194			7,091			7,521			7,496			7,938
Net loss per share, basic and diluted⁽⁶⁾	$	(2.50	)	$	(0.83	)	$	(0.52	)	$	(0.46	)	$	(0.60	)



Pro forma weighted average shares outstanding⁽⁶⁾								29,921						32,473
Pro forma net loss per share⁽⁶⁾							$	(0.13	)				$	(0.13	)

To supplement our consolidated financial statements, which are prepared and presented in accordance with GAAP, we use certain non-GAAP financial measures, as described below, to understand and evaluate our core operating performance. These non-GAAP financial measures, which may be different than similarly titled measures used by other companies, are presented to enhance investors' overall understanding of our financial performance and should not be considered a substitute for, or superior to, the financial information prepared and presented in accordance with GAAP.

We believe that these non-GAAP financial measures provide useful information about our financial performance, enhance the overall understanding of our past performance and future prospects, and allow for greater transparency with respect to important metrics used by our management for financial and operational decision-making. We are presenting these non-GAAP financial metrics to assist investors in seeing our financial performance through the eyes of management, and because we believe that these

measures provide an additional tool for investors to use in comparing our core financial performance over multiple periods with other companies in our industry.

We use the non-GAAP financial measure of adjusted net income (loss), which is defined as GAAP net income (loss), excluding stock-based compensation expense, restructuring expense, costs associated with mergers and acquisitions, warrant interest expense and non-capitalizable costs associated with this initial public offering. Due to our significant federal and state net operating loss carryforwards, as well as a full valuation against our net deferred tax assets, there is no income tax effect on adjusted net income (loss) in the presented periods. We believe that adjusted net income (loss) helps identify underlying trends in our business that could otherwise be masked by the effect of the expenses that we exclude in adjusted net income (loss). Additionally, our executive compensation structure uses an adjusted net income (loss) target as one of the components when calculating payments that have been earned.

The following table presents a reconciliation of net loss, the most directly comparable financial measure calculated in accordance with GAAP, to adjusted net income (loss), for each of the periods presented:

There are a number of limitations related to the use of adjusted net income (loss) as compared to net loss, including that adjusted net income (loss) excludes stock-based compensation expense, which has been, and will continue to be for the foreseeable future, a significant recurring expense in our business and an important part of our compensation strategy.

We use the non-GAAP financial measure of free cash flow, which is defined as GAAP net cash flows from operating activities, reduced by purchase of property and equipment, and principal payments on capital lease obligations. We believe free cash flow is an important liquidity measure of the cash that is available, after capital expenditures, for operational expenses, investment in our business and to make acquisitions. Free cash flow is useful to investors as a liquidity measure because it measures our ability to

generate or use cash. Once our business needs and obligations are met, cash can be used to maintain a strong balance sheet and invest in future growth.

The following table presents a reconciliation of net cash from operating activities, the most directly comparable financial measure calculated in accordance with GAAP, to free cash flow for each of the periods presented:

There are a number of limitations related to the use of free cash flow as compared to net cash from operating activities, including that free cash flow does not reflect future contractual commitments.

MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS

You should read the following discussion and analysis of our financial condition and results of operations together with our consolidated financial statements and the related notes and other financial information included elsewhere in this prospectus. Some of the information contained in this discussion and analysis or set forth elsewhere in this prospectus, including information with respect to our plans and strategy for our business, includes forward-looking statements that involve risks and uncertainties. You should review the sections titled "Special Note Regarding Forward-Looking Statements" and "Risk Factors" for a discussion of important factors that could cause actual results to differ materially from the results described in or implied by the forward-looking statements contained in the following discussion and analysis.

SendGrid was started by three developers who found themselves spending an increasing amount of time resolving email issues rather than working on the core products of their emerging technology companies. Frustrated with the time and effort required to send email at scale, they started our company with the goal of building an effective and easy to adopt platform for scalable email delivery. Since our founding, we have focused on extending the scale and reliability of our platform while expanding the scope of our offerings. We introduced our Email API service in 2009, which allowed businesses to send both transactional and marketing emails. We continued to add functionality to our platform and in late 2015 introduced our Marketing Campaigns service, which allows marketers to upload and manage customer contact lists, create and test email templates, and then execute and analyze multi-faceted email campaigns that engage customers and drive growth. In 2016, we introduced Expert Services to help businesses further optimize the deliverability of their emails and the effectiveness of their email marketing programs.

Our services are designed to be easy to adopt and affordable for businesses of all sizes. Our services are easily accessible from our website, with transparent pricing and a monthly contract term. Our customers pay for what they need and can begin using our services in minutes. We generate revenue primarily through sales of subscriptions to our services. We offer our Email API service on a subscription basis, priced based on email volume. Our Email API service pricing plans start at $9.95 per month for up to 40,000 emails. Our Marketing Campaigns service is priced based on the number of email contacts stored on our platform and the number of monthly emails sent to those contacts through our Email API service. Our Marketing Campaigns service is fully integrated, such that businesses using the service to store email contacts on our system must also use our Email API to send email to those contacts. Therefore, revenue from our Marketing Campaigns service includes revenue generated from subscriptions by our Marketing Campaigns customers both to store email contacts on our system and to send emails through our Email API service to those contacts. Expert Services are charged either on a monthly basis or as a one-time consultation fee and to date has accounted for a de minimus percentage of our total revenue.

We primarily sell to developers and marketers who want easy to use, self-service tools. Businesses learn about us through our marketing efforts or through our user community and sign up through our website. We offer documentation to enable self-service onboarding and 24 x 7 support to answer questions. We also sell our services to and through leading public cloud infrastructure providers and ecommerce platforms, such as Heroku, Amazon Web Services and Microsoft Azure, software vendors that offer complementary products and with which we co-sell our Email API and Marketing Campaigns services, such as Github, New Relic and Twilio, and digital marketing agencies, such as Deloitte Digital, which resell

our services to their clients. Additionally, we have a limited inside sales team to manage inbound interest from businesses.

We target any business that needs to deliver transactional or marketing email. As a result, our customers include SMBs and large enterprises across a wide range of industries. As of September 30, 2017, we had more than 58,000 customers globally. We believe a relatively small number of these businesses have more than one unique paying account with us, and we count each of these accounts as a separate customer. No single customer represented more than 2% of annual total revenue in 2014, 2015 or 2016 or for the nine months ended September 30, 2017, and our ten largest customers comprised 10% or less of our total revenue in each of 2014, 2015 and 2016 and for the nine months ended September 30, 2017.

We have a history of attracting new customers that increase their spend with us over time. Our customers generally increase spend as their businesses grow, they send more email, or as they expand their use of our services. The chart below illustrates the annual total revenue from each customer cohort over the years presented. Each cohort represents customers that made their initial purchase from us in a given year. For example, the 2012 cohort represents all customers that made their initial purchase from us between January 1, 2012 and December 31, 2012. The 2012 cohort increased their contribution to our annual total revenue from $4.8 million in 2012 to $15.4 million in 2016, growing by 221% over that five-year period.

Our historical revenue has generally grown linearly throughout the quarter, as shown by the chart below. Because we utilize a self-service model, customers generally sign up for our services on our website without interacting with anyone at the company, as we do not have a traditional enterprise salesforce.

We have achieved significant growth in recent periods. For 2014, 2015, 2016 and the nine months ended September 30, 2017:

We had over 58,000 customers globally as of September 30, 2017. We believe we are less than 3% penetrated in our potential addressable customer base. Our revenue grows as our customers scale and send more email. Our typical adoption pattern begins with a developer who signs up for our Email API service. Once a customer begins using our Email API service, the customer often increases the number of emails sent through our service over time, principally as a result of the customer's organic growth and also through the adoption of additional use cases and services, in each case typically without significant incremental marketing expenditures from us.

Since launching our Marketing Campaigns service in late 2015, we have seen strong receptivity from marketers, with over 8,600 customers using the service as of September 30, 2017. We intend to grow our Marketing Campaigns business by adding new Marketing Campaigns customers and by cross selling into our existing Email API service customer base. Many of our customers using our Email API service for transactional email do not use a separate, dedicated marketing product, and we believe that our Marketing Campaigns service offers them a highly attractive proposition. The growth of our business is dependent on our ability to attract and retain new customers and to expand services with existing customers.

Customers outside the United States are increasingly using our services. We define U.S. revenue as revenue derived from customers with U.S. billing addresses and international revenue as all other revenue. In each of 2014, 2015 and 2016, more than 36% of our total revenue was from outside the United States, and during that period our international revenue increased by $13.5 million, or approximately 84%. Recently, we opened our first international sales and marketing office, located in London. We plan to grow our international revenue by expanding our sales and marketing efforts in select countries and regions, through increased leverage with international strategic partners, and through localization of our services and support.

We have relied primarily on our self-service sales model and relationships with strategic partners to attract international customers. We have limited international infrastructure, limited experience operating directly in international markets and no localization of our services or support. To the extent that our self-service sales model or strategic partner relationships do not continue to allow us to attract international customers, our international revenue may not grow or may decline, or we may incur significant additional selling and marketing and other expenses in order to grow our international revenue, including as a result of any expansion of our direct sales force outside the United States. Furthermore, our ability to successfully localize our services and support without making additional material investments in international infrastructure and personnel is uncertain. To the extent that increased costs from our international expansion are not offset by sufficient revenue growth, our profitability will be harmed. See "Risk Factors—Our future success depends in part on our ability to continue to drive adoption of our platform and services by international customers, and our international operations and sales to customers with international operations expose us to risks inherent in international sales" for additional information.

We have established strategic relationships with a number of other companies and we intend to continue to invest in, and expand, such relationships. Our partner ecosystem includes strategic relationships with leading public cloud infrastructure providers and ecommerce platforms, software vendors that offer complementary products and with which we co-sell our Email API and Marketing Campaigns services, and digital marketing agencies, which resell our services to their clients. Sales to or

through these strategic partners accounted for 3%, 4% and 5% of our total revenue in 2015, 2016 and the nine months ended September 30, 2017, respectively. Increased sales through our strategic partners will have an impact on our revenue growth and operating margin.

Given our volume pricing model, our revenue is directly correlated with the number of emails sent by our customers. During the fourth-quarter holiday season, our customers process a relatively higher number of transactions, run a greater number of marketing programs, and therefore send more emails. Partially because of this seasonality, a greater percentage of our annual revenue has come from our fourth quarter than from other quarters. In each of 2014, 2015 and 2016, 28% to 29% of our annual revenue was in our fourth quarter. While we believe that this seasonality has affected and will continue to affect our quarterly results, our rapid growth has largely masked seasonal trends to date. Seasonality may become more pronounced in the future to the extent our revenue mix shifts between our Email API, Marketing Campaigns and other revenue sources over time.

We regularly review the following key metrics to measure performance, identify trends, formulate financial projections and make strategic decisions. We are not aware of any uniform standards for calculating these key metrics. In addition, other companies may not calculate similarly titled metrics in a consistent manner, which may hinder comparability.

We believe that the size of our customer base is an important indicator of the growth of our business, the market acceptance of our platform and future revenue trends. We define a customer as any user account from which we derive revenue during the last month of the period. We believe a relatively small number of businesses have more than one unique paying account with us, and we count each of these accounts as a separate customer. More specifically, for each of the periods presented, we estimate that approximately 4% of our customers may have been part of the same business as one or more of our other customers. Any such affiliations among our customers do not impact how we manage our business or our customer relationships or how our operating results are reported. We view our total number of customers, irrespective of any affiliations among them, as reflective of the number of sources of revenue to us and our growth and potential for future growth because each customer reported is making a separate purchasing decision with respect to our services. Furthermore, in general, we count each of our strategic partners as a single customer regardless of how many end customers the strategic partner may have that are using our services.

We believe email volume is an important measure of our business because it is a key indicator of volume growth and our ability to generate revenue, since a substantial majority of our revenue is based on the number of emails processed. Email volume consists of the total number of emails we processed in a given period.

The graphic below on the left shows the growth in our number of customers (in thousands) through September 30, 2017. The graphic below on the right shows the growth in our quarterly email volume (in

billions) through September 30, 2017 and illustrates seasonal trends in email volume, as discussed in the section titled "—Key Factors Affecting Our Performance—Seasonality."

We believe subscription net dollar retention rate is an important measure for evaluating our business because it quantifies the impact on revenue growth of both retention and expansion of our existing customers.

Our ability to drive growth and generate incremental revenue depends, in part, on our ability to retain our customers and increase their use of our platform. An important way in which we track our performance in this area is by measuring subscription net dollar retention rate.

Our subscription net dollar retention rate increases when our customers increase their volume usage of our Email API service or extend usage of our platform. Our subscription net dollar retention rate decreases when customers temporarily or permanently cease or reduce volume usage of our Email API service or otherwise cease or reduce usage of our platform. Changes in our pricing may materially impact our subscription net dollar retention rate in the future, but did not have a material impact for any of the periods presented.

Our subscription net dollar retention rate compares the subscription revenue from a set of customers in a period to the same period in the prior year. To calculate the subscription net dollar retention rate for a period, we first identify the cohort of customers that were customers in the equivalent prior year period. Subscription net dollar retention rate for a period is the quotient obtained by dividing the subscription revenue generated from that cohort in a period, by the subscription revenue generated from that same cohort in the corresponding prior year period.

Alternatively, our subscription net dollar retention rate can be calculated as the difference between our subscription dollar expansion rate and our subscription gross dollar churn rate. Our subscription dollar expansion rate is indicative of net revenue growth period over period from customers that contribute revenue in both the measured period and the equivalent prior year period. We calculate subscription dollar expansion rate for a period in two steps: first, we take the increase or decrease in the subscription revenue in a period from customers that contributed revenue in both that period and the same period in the prior year and add the total subscription revenue in the prior year period; and second, we divide the result of the first step by the total subscription revenue in the prior year period. Our subscription gross dollar churn rate is indicative of lost revenue from customers that contribute no revenue in the measured period but did contribute revenue in the equivalent prior year period. We also calculate subscription gross dollar churn rate in a period in two steps: first, we measure the amount of subscription revenue in the same period in

the prior year from customers that contributed revenue in the prior year period but did not contribute revenue in the given period; and second, we divide the result of the first step by the total subscription revenue in the equivalent prior year period.

For 2014, 2015, 2016 and the nine months ended September 30, 2016 and September 30, 2017, our subscription dollar expansion rate was 129%, 124%, 122%, 121% and 126%, respectively, and our subscription gross dollar churn rate was 13%, 12%, 11%, 11% and 10%, respectively. Our subscription net dollar retention rate for those periods is set forth in the table below.

The following are our key metrics as of and for each of 2014, 2015, 2016 and the nine months ended September 30, 2016 and September 30, 2017.

We generate revenue primarily through the sale of our Email API and Marketing Campaigns services, which we sell on a monthly subscription basis. Sales of our Email API service accounted for 79%, 79%, 79% and 80% of our total revenue in 2014, 2015, 2016 and the nine months ended September 30, 2017, respectively. Other sources of revenue for these periods consisted of sales of our email marketing services, including sales of our Marketing Campaigns service and its predecessor, and other sources, including professional services. Sales of our Marketing Campaigns service accounted for 0%, 1%, 9% and 12% of our total revenue in 2014, 2015, 2016 and the nine months ended September 30, 2017, respectively. Revenue attributed to sales of our Email API service does not include the portion of revenue generated by subscriptions by our email marketing services customers to send emails through our Email API to contacts stored on our system for use with our email marketing services.

Our customers subscribe to our Email API service through a plan that provides for a predetermined allowance of renewable email credits to be used each month. Usage above the plan's credit allowance is billed as an overage charge. All plans include basic customer support.

Certain customers also subscribe to our Marketing Campaigns service. Our customers store email contacts and segmentation information on our platform in order to customize communications.

Cost of revenue consists principally of depreciation and amortization expense related to hosting equipment and outsourced managed hosting costs. Other components include employee related costs, including salaries, bonuses, benefits, stock-based compensation, other related costs, and an allocation of our general overhead. We expect our cost of revenue to continue to increase in absolute dollar amounts as we invest in our business.

Gross profit is total revenue less total cost of revenue. Gross margin is gross profit expressed as a percentage of total revenue. We expect that gross profit and gross margin will continue to be affected by various factors including our pricing, our mix of services sold and our ability to increase total revenue at a sufficient rate to cover fixed costs.

Our operating expenses consist of research and development, selling and marketing, and general and administrative expenses.

Research and development expense consists primarily of employee related costs, including salaries, bonuses, benefits, stock-based compensation, other related costs, and an allocation of our general overhead. Also included are non-personnel costs, such as subcontracting, consulting and professional fees for third party development resources and depreciation costs. Our research and development efforts focus on maintaining and enhancing functionality of existing services and adding new features and services. We expect research and development expense to increase in absolute dollars as we invest in the enhancement of our services.

Selling and marketing expense consists primarily of employee related costs, including salaries, bonuses, benefits, stock-based compensation, other related costs, and an allocation of our general overhead. These expenses also include expenditures related to advertising, marketing, promotional events, and brand awareness activities. We expect selling and marketing expense to continue to increase in absolute dollars as we enhance our services and implement new marketing strategies.

General and administrative expense consists primarily of employee related costs, including salaries, bonuses, benefits, stock-based compensation, other related costs, and an allocation of our general overhead for those employees associated with administrative services such as legal, human resources, information technology, accounting, and finance. These expenses also include certain third-party consulting services, certain facilities costs, credit card processing fees, and any corporate overhead costs not allocated to other expense categories.

We expect our general and administrative expense to increase in absolute dollars as we continue to grow our business. We also anticipate that we will incur additional costs for employees and third-party consulting services related to preparation to become and operate as a public company.

The following table sets forth our consolidated statements of operations data for the periods indicated:

	For the Year Ended December 31,									For the Nine Months Ended September 30,

	2014			2015			2016			2016			2017
	(in thousands)
Consolidated Statements of Operations Data:
Revenue	$	42,776		$	58,476		$	79,929		$	56,858		$	80,159
Cost of revenue⁽¹⁾⁽²⁾		15,187			18,961			21,605			15,995			21,357

Gross profit		27,589			39,515			58,324			40,863			58,802

Operating Expenses:⁽¹⁾⁽²⁾
Research and development		15,290			18,959			21,178			15,632			21,208
Selling and marketing		15,260			13,737			21,800			15,311			20,582
General and administrative⁽³⁾⁽⁴⁾		9,550			12,477			18,920			13,091			21,222
Loss on disposal of assets		63			1			27			27			2

Total operating expenses		40,163			45,174			61,925			44,061			63,014

Loss from operations		(12,574	)		(5,659	)		(3,601	)		(3,198	)		(4,212	)

Other income (expense), net⁽⁵⁾		(386	)		(195	)		(307	)		(285	)		(515	)
Net loss before provision for income taxes	$	(12,960	)	$	(5,854	)	$	(3,908	)	$	(3,483	)	$	(4,727	)
Provision for income taxes		—			—			—			—			—

Net loss	$	(12,960	)	$	(5,854	)	$	(3,908	)	$	(3,483	)	$	(4,727	)

The following table sets forth our consolidated statements of operations data expressed as a percentage of total revenue:

	For the Year Ended December 31,									For the Nine Months Ended September 30,

	2014			2015			2016			2016			2017
Consolidated Statements of Operations Data:
Revenue		100	%		100	%		100	%		100	%		100	%
Cost of revenue		36			32			27			28			27

Gross margin		64			68			73			72			73

Operating Expenses:
Research and development		36			32			26			27			26
Selling and marketing		36			23			27			27			26
General and administrative		22			21			24			23			26
Loss on disposal of assets		—			—			—			—			—

Total operating expenses		94			77			77			77			79

Loss from operations		(29	)		(10	)		(5	)		(6	)		(5	)
Other income (expense), net		(1	)		—			—			(1	)		(1	)
Net loss before provision for income taxes		(30	)		(10	)		(5	)		(6	)		(6	)
Provision for income taxes		—			—			—			—			—

Net loss		(30	)%		(10	)%		(5	)%		(6	)%		(6	)%

Total revenue increased $23.3 million, or 41%, in the nine months ended September 30, 2017, compared to the nine months ended September 30, 2016. The increase was attributable to an increase in email volume from, and sales of additional services to, existing customers and sales of our Email API service and other services to new customers. Revenue from existing customers comprised $17.8 million, or 76%, of the $23.3 million increase, with the remaining increase attributed to revenue from new customers. Our overall email volume increased to 325 billion in the first nine months of 2017 from 237 billion in the same period in 2016 and our number of customers increased by 36% from September 30, 2016 to September 30, 2017. Revenue from our Email API service increased by $18.7 million, or 42%, in the nine months ended September 30, 2017, compared to the nine months ended September 30, 2016. Revenue

from email marketing services, including our Marketing Campaigns service and its predecessor, increased by $3.4 million, or 33%, in the nine months ended September 30, 2017, compared to the nine months ended September 30, 2016, as a result of a $5.1 million increase in revenue from our Marketing Campaigns service in the nine months ended September 30, 2017, offset by a $1.7 million decrease in revenue from our predecessor email marketing service. A portion of the increase in our Marketing Campaigns service revenue is attributable to sales to customers that converted to our Marketing Campaigns service from its predecessor following our announcement that we would phase out our predecessor email marketing service in 2017.

Cost of revenue increased $5.4 million, or 34%, in the nine months ended September 30, 2017, compared to the nine months ended September 30, 2016. This increase was attributable to a $2.7 million increase in data center and hosting costs due to additional property and equipment used to support growth of the business, as well as a $2.7 million increase in employee related costs due to an increase in headcount related to delivering our services and supporting our customers. There was also an increase of $0.5 million in other expenses, including allocated overhead. These increases were partially offset by a decrease in costs related to third-party consulting services of $0.5 million.

Gross margin increased to 73% in the nine months ended September 30, 2017 compared to 72% in the nine months ended September 30, 2016 primarily due to total revenue increasing at a higher rate than the associated costs.

Research and development expense increased $5.6 million, or 36%, in the nine months ended September 30, 2017, compared to the nine months ended September 30, 2016. This increase was due to a $4.6 million increase in employee related costs due to an increase in headcount to support additional research and development initiatives and a $0.7 million increase in other expenses, including allocated overhead. The remaining increase of $0.3 million was related to merger and acquisition costs.

Selling and marketing expense increased $5.3 million, or 34%, in the nine months ended September 30, 2017, compared to the nine months ended September 30, 2016. This increase was due to a $2.6 million increase in advertising and promotion expense, a $2.0 million increase in employee related costs related to increased headcount, and a $0.8 million increase in other expenses, including allocated overhead. These increases were partially offset by a decrease in costs related to third-party consulting services of $0.1 million.

General and administrative expense increased $8.1 million, or 62%, in the nine months ended September 30, 2017, compared to the nine months ended September 30, 2016. This increase was attributable to a $4.1 million increase in employee related costs, largely due to an increase in headcount to support the growth of our business, a $1.0 million increase in costs related to our planned initial public offering, a $1.0 million increase in restructuring expense related to the relocation of our headquarters, a $0.5 million increase in credit card fees, a $0.4 million increase in office expense, a $0.4 million increase in sales tax expense, and a $1.0 million increase in other expenses, including allocated overhead. These increases were partially offset by a $0.3 million decrease in travel and entertainment expense.

Total revenue increased $21.5 million, or 37%, in 2016, compared to 2015. The increase was attributable to an increase in email volume from, and sales of additional services to, existing customers and sales of our Email API service and other services to new customers. Revenue from existing customers comprised $12.3 million, or 57%, of the $21.5 million increase, with the remaining increase attributed to revenue from new customers. Our overall email volume increased to 338 billion in 2016 from 233 billion in 2015 and our number of customers increased by 37% from December 31, 2015 to December 31, 2016. Revenue from our Email API service increased by $17.4 million, or 38%, in 2016, compared to 2015. Revenue from our email marketing services, including our Marketing Campaigns service and its predecessor, increased by $3.0 million, or 26%, in 2016, compared to 2015, as a result of a $6.3 million increase in revenue from our Marketing Campaigns service in 2016, offset by a $3.3 million decrease in revenue from our predecessor email marketing service. The increase in revenue from our Marketing Campaigns service resulted from our offering the service for the full year in 2016 following its introduction in late 2015 and sales to new and existing customers, a portion of which were users of our predecessor email marketing service.

Total revenue increased $15.7 million, or 37%, in 2015, compared to 2014. The increase was attributable to an increase in email volume from, and sales of additional services to, existing customers and sales of our Email API service and other services to new customers. Revenue from existing customers comprised $10.0 million, or 64%, of the $15.7 million increase, with the remaining increase attributed to

revenue from new customers. Our overall email volume increased to 233 billion in 2015 from 161 billion in 2014 and our number of customers increased by 17% from December 31, 2014 to December 31, 2015. Revenue from our Email API service increased by $12.3 million, or 36%, in 2015, compared to 2014. Revenue from our email marketing services, including our Marketing Campaigns service and its predecessor, increased by $2.9 million, or 33%, in 2015, compared to 2014. We launched our Marketing Campaigns service in 2015 and accordingly had no Marketing Campaigns revenue in 2014.

Cost of revenue increased $2.6 million, or 14%, in 2016, compared to 2015. The increase was primarily attributable to a $1.4 million increase in data center and hosting costs due to additional property and equipment used to support growth of the business, as well as a $1.2 million increase in employee related costs due to an increase in headcount related to delivering our services and supporting our customers.

Cost of revenue increased $3.8 million, or 25%, in 2015, compared to 2014. The increase was primarily attributable to a $2.2 million increase in data center and hosting costs due to additional property and equipment used to support growth of the business, as well as a $1.0 million increase in employee related costs, a $0.5 million increase in costs related to third-party consulting services and a $0.1 million increase in other expenses, including allocated overhead.

Research and development expense increased $2.2 million, or 12%, in 2016 compared to 2015. This increase was primarily a result of a $2.9 million increase in engineering employee related costs related to additional research and development initiatives, partially offset by a $0.4 million decrease in other expenses, including allocated overhead, and a decrease in costs related to third-party consulting services of $0.3 million.

Research and development expense increased $3.7 million, or 24%, in 2015 compared to 2014. This increase was a result of a $5.4 million increase in engineering employee related costs related to additional research and development initiatives, a $0.3 million increase in office expense, and a $0.3 million increase in business operations expense and software costs. These increases were partially offset by a decrease in costs related to third-party consulting services of $2.3 million.

Selling and marketing expense increased $8.1 million, or 59%, in 2016 compared to 2015. This increase was a result of a $3.9 million increase in employee related costs due to an increase in headcount, a $3.0 million increase in advertising and promotion expense due to implementation of a new advertising strategy, a $0.6 million increase in costs related to third-party consulting services, and a $0.6 million increase in other expenses, including allocated overhead.

Selling and marketing expense decreased $1.5 million, or 10%, in 2015 compared to 2014. This decrease was a result of a $0.6 million decrease in costs related to third-party consulting services, a $0.5 million decrease in employee related costs and a $0.4 million decrease in travel and entertainment expense.

General and administrative expense increased $6.4 million, or 52%, in 2016 compared to 2015. This increase was a result of a $2.7 million increase in employee related costs, a $0.9 million increase in office expense, a $0.7 million increase in third-party consulting services, a $0.5 million increase in credit card fees, a $0.4 million increase in software expense, a $0.4 million increase in costs related to business operations, and a $0.8 million increase in restructuring expense related to the relocation of our headquarters and other expenses, including allocated overhead.

General and administrative expense increased $2.9 million, or 31%, in 2015 compared to 2014. This increase was a result of a $1.5 million increase in employee related costs to support the increased scale of our business, a $0.3 million increase in travel and entertainment expense, a $0.4 million increase in credit card fees, and a $0.7 million increase in other expenses, including allocated overhead.

The following tables set forth unaudited quarterly statements of operations data for each of the eleven quarters in the period ended September 30, 2017. The information for each of these quarters has been prepared on the same basis as the audited annual consolidated financial statements included elsewhere in this prospectus and, in the opinion of management, includes all adjustments, which consist only of normal recurring adjustments, necessary for the fair presentation of the results of operations for these periods. This data should be read in conjunction with our consolidated financial statements, related notes and other financial information included elsewhere in this prospectus. Our quarterly results of operations will vary in the future. These quarterly results are not necessarily indicative of our operating results to be expected for 2017 or any other future period.


Copies to:
Michael L. Platt Eric C. Jensen Matthew P. Dubofsky Cooley LLP 380 Interlocken Crescent, Suite 900 Broomfield, CO 80021 (720) 566-4000	Michael Tognetti General Counsel SendGrid, Inc. 1801 California Street, Suite 500 Denver, CO 80202 (888) 985-7363	Sarah K. Solum Davis Polk & Wardwell LLP 1600 El Camino Real Menlo Park, CA 94025 (650) 752-2000


Large accelerated filer o		Accelerated filer o		Non-accelerated filer ý (Do not check if a smaller reporting company)		Smaller reporting company o Emerging growth company ý

Title of Each Class of Securities to be Registered	Amount to be Registered⁽¹⁾	Proposed Maximum Offering Price Per Share	Proposed Maximum Aggregate Offering Price⁽²⁾	Amount of Registration Fee⁽³⁾




Common Stock, $0.001 par value per share	8,855,000	$15.50	$137,252,500	$17,088

	Price to Public	Underwriting Discounts and Commissions⁽¹⁾	Proceeds to SendGrid

Per Share	$	$	$
Total	$	$	$


William Blair		KeyBanc Capital Markets		Piper Jaffray		Stifel


Delaware (State or other jurisdiction of incorporation or organization)		7372 (Primary Standard Industrial Classification Code Number)		27-0554600 (I.R.S. Employer Identification Number)

		Page

Prospectus Summary			1
Risk Factors			15
Special Note Regarding Forward-Looking Statements			48
Market and Industry Data			50
Use of Proceeds			51
Dividend Policy			52
Capitalization			53
Dilution			56
Selected Consolidated Financial Data			59
Management's Discussion and Analysis of Financial Condition and Results of Operations			63
Letter from Our CEO			90
Business			94
Management			113
Executive Compensation			121
Certain Relationships and Related Party Transactions			133
Principal Stockholders			137
Description of Capital Stock			141
Shares Eligible for Future Sale			146
Material U.S. Federal Income Tax Considerations for Certain Non-U.S. Holders			148
Underwriters			152
Legal Matters			160
Experts			160
Where You Can Find Additional Information			160
Index to Financial Statements			F-1


Assumed initial public offering price per share			$	14.50
Pro forma net tangible book value per share as of September 30, 2017	$	1.19
Increase in pro forma net tangible book value per share as of September 30, 2017		2.26

Pro forma as adjusted net tangible book value per share immediately after this offering				3.45

Dilution per share to new investors participating in this offering			$	11.05

	Shares purchased					Total consideration

	Shares purchased					Total consideration					Average price per share
	Number		Percent			Amount		Percent			Average price per share
Existing stockholders		32,591,661		81	%	$	82,651,681		43	%	$	2.54
New investors		7,700,000		19			111,650,000		57		$	14.50

Total		40,291,661		100	%	$	194,301,681		100	%

	As of Dec. 31,

	As of Dec. 31,						As of Sep. 30, 2017
	2015			2016			As of Sep. 30, 2017
	(in thousands)
Consolidated Balance Sheet Data:
Cash and cash equivalents	$	9,269		$	40,400		$	37,397
Working capital		5,665			33,775			29,955
Property and equipment, net		10,413			19,190			26,322
Total assets		24,676			66,635			79,748
Total stockholders' deficit	$	(35,947	)	$	(37,780	)	$	(38,999	)

	For the Nine Months Ended September 30,

	2016		2017		$ Change		% Change
	(dollars in thousands)
Revenue	$	56,858	$	80,159	$	23,301		41	%

	For the Three Months Ended

	Mar. 31, 2015		Jun. 30, 2015		Sep. 30, 2015		Dec. 31, 2015		Mar. 31, 2016		Jun. 30, 2016		Sep. 30, 2016		Dec. 31, 2016		Mar. 31, 2017		Jun. 30, 2017		Sep. 30, 2017
	(in thousands)
Consolidated Statements of Operations Data:
Revenue	$	12,885	$	14,146	$	14,985	$	16,460	$	17,125	$	19,032	$	20,701	$	23,071	$	24,831	$	27,012	$	28,316
Cost of revenue		4,258		4,517		4,891		5,295		5,237		5,366		5,392		5,610		6,471		7,274		7,612

Gross profit		8,627		9,629		10,094		11,165		11,888		13,666		15,309		17,461		18,360		19,738		20,704


Morgan Stanley		J.P. Morgan