X0306 4 2021-07-01 0 0001644675 Mimecast Ltd MIME 0001642308 Raissipour David C/O MIMECAST NORTH AMERICA, INC. 191 SPRING STREET LEXINGTON MA 02421 0 1 0 0 Chief Tech. & Product Officer Restricted Share Units 2021-07-01 4 A 0 56401 0.00 A 56401 D Share Option (Right to Buy) 53.19 2021-07-01 4 A 0 124505 0.00 A 2031-07-01 Ordinary Shares 124505 124505 D 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 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. This option was granted on July 1, 2021. Twenty-five percent (25%) of the shares vest on July 1, 2022, and the remainder of the shares vest on a quarterly 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 July 2, 2021). /s/ Robert P. Nault, Attorney-in-Fact 2021-07-06