X0306 4 2022-02-01 0 0001644675 Mimecast Ltd MIME 0001762176 Anderson Karen M. C/O MIMECAST NORTH AMERICA, INC. 191 SPRING STREET LEXINGTON MA 02421 0 1 0 0 Chief Human Resources Officer Ordinary Shares 2022-02-01 4 M 0 4333 A 4333 D Restricted Share Units 2022-02-01 4 F 0 1917 79.74 D 10583 D Restricted Share Units 2022-02-01 4 M 0 4333 D 6250 D Restricted Share Units 9549 D Restricted Share Units 12239 D Restricted Share Units 9400 D The number of Ordinary Shares reflects the settlement of restricted share units upon vesting, net of Ordinary Shares that were retained (but not issued) by the Issuer in satisfaction of tax withholding obligations associated with the vesting of such units. Each restricted share unit represents a contingent right to receive one share of the Issuer's Ordinary Shares. The restricted share units reported as disposed of herein reflect the number of Ordinary Shares underlying the restricted share units that were retained (but not issued) by the Issuer in satisfaction of tax withholding obligations associated with the vesting of such units. Price reflects the closing price of the Issuer's Ordinary Shares on the Nasdaq Global Select Market on February 1, 2022. These restricted share units were granted on February 1, 2019. Twenty-five percent (25%) of the units vested on February 1, 2020, twenty-five percent (25%) of the units vested on February 1, 2021, twenty-five percent (25%) of the units vested on February 1, 2022, and the remainder of the units vest on February 1, 2023, provided that the Reporting Person remains an employee of the Issuer on such vesting date. The restricted share units reported as disposed of herein were settled for the Issuer's Ordinary Shares upon the vesting of such units (as reported in Row 1 above). These restricted share units were granted on April 1, 2020. Twenty-five percent (25%) of the units vested on April 1, 2021, and the remainder of the units vest on an annual basis over the next three (3) years, provided that the Reporting Person remains an employee of the Issuer on each such vesting date. These restricted share units were granted on April 1, 2021. Twenty-five percent (25%) of the units vest on April 1, 2022 and the remainder of the units vest on an annual basis over the next three (3) years, provided that the Reporting Person remains an employee of the Issuer on each such vesting date. These restricted share units were granted on July 1, 2021. Twenty-five percent (25%) of the units vest on July 1, 2022 and the remainder of the units vest on an annual basis over the next three (3) years, provided that the Reporting Person remains an employee of the Issuer on each such vesting date. Exhibit 24 Power of Attorney (incorporated by reference to Power of Attorney filed as Exhibit 24 to Form 3 filed by the Reporting Person on January 3, 2019). /s/ Robert P. Nault, Attorney-in-Fact 2021-02-02