X0306 4 2021-05-03 0 0001644675 Mimecast Ltd MIME 0001789268 DiMarino Dino C/O MIMECAST NORTH AMERICA, INC. 191 SPRING STREET LEXINGTON MA 02421 0 1 0 0 Chief Revenue Officer Restricted Share Units 2021-05-03 4 A 0 28510 A 28510 D Ordinary Shares 13656 D Restricted Share Units 1875 D Restricted Share Units 7500 D Restricted Share Units 11250 D Restricted Share Units 22469 D Restricted Share Units 29375 D These restricted share units were granted on May 3, 2021. Twenty-five percent (25%) of the units vest on May 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. Each restricted share unit represents a contingent right to receive one share of the Issuer's Ordinary Shares. These restricted share units were granted on April 2, 2018. Twenty-five percent (25%) of the units vested on April 2, 2019, twenty-five percent (25%) of the units vested on April 2, 2020, twenty-five percent (25%) of the units vested on April 2, 2021, and the remainder of the units vest on April 2, 2022, provided that the Reporting Person remains an employee of the Issuer on such vesting date. These restricted share units were granted on April 1, 2019. Twenty-five percent (25%) of the units vested 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 two (2) years, provided that the Reporting Person remains an employee of the Issuer on each such vesting date. These restricted share units were granted on October 1, 2019. Twenty-five percent (25%) of the units vested on October 1, 2020, 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, 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. 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 October 1, 2019). /s/ Robert P. Nault, Attorney-in-Fact 2021-05-03