X0306 4 2021-10-06 0 0001644675 Mimecast Ltd MIME 0001838194 Auriol Potier Helene C/O MIMECAST NORTH AMERICA, INC. 191 SPRING STREET LEXINGTON MA 02421 1 0 0 0 Restricted Share Units 2021-10-06 4 A 0 2742 0.00 A 2742 D Restricted Share Units 3700 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 October 6, 2021 and vest in full on the one year anniversary of the date of grant, provided that the Reporting Person remains a director of the Issuer on such vesting date. The number of restricted share units issued under this grant was determined on January 4, 2021, and 1,233 units vest on January 1, 2022, 1,233 units vest on January 1, 2023 and 1,234 units on January 1, 2024, provided that the Reporting Person remains a director of the Issuer on 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 4, 2021). /s/ Robert P. Nault, Attorney-in-Fact 2021-10-08