X0306 4 2022-02-28 0 0001644675 Mimecast Ltd MIME 0001588892 Brown Rafeal E. C/O MIMECAST NORTH AMERICA, INC. 191 SPRING STREET LEXINGTON MA 02421 0 1 0 0 Chief Financial Officer Ordinary Shares 2022-02-28 4 S 0 5 79.515 D 23765 D Ordinary Shares 2022-04-01 4 M 0 18977 A 42742 D Restricted Share Units 2022-04-01 4 F 0 3763 79.59 D 21237 D Restricted Share Units 2022-04-01 4 M 0 8737 D 12500 D Restricted Share Units 2022-04-01 4 F 0 3820 79.59 D 22019 D Restricted Share Units 2022-04-01 4 M 0 4792 D 17227 D Restricted Share Units 2022-04-01 4 F 0 4343 79.59 D 34824 D Restricted Share Units 2022-04-01 4 M 0 5448 D 29376 D The number of Ordinary Shares reflects the aggregate settlement of the three (3) restricted share units reported below 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 April 1, 2022. 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, twenty-five percent (25%) of the units vested on April 1, 2022, and the remainder of the units vest on April 1, 2023, provided that the Reporting Person remains an employee of the Issuer on each 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 2 above). These restricted share units were granted on April 1, 2020. Twenty-five percent (25%) of the units vested on April 1, 2021, twenty-five percent (25%) of the units vested on April 1, 2022 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 April 1, 2021. Twenty-five percent (25%) of the units vested 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 March 18, 2019). /s/ Robert P. Nault, Attorney-in-Fact 2022-04-04