X0306 4 2021-10-06 0 0001644675 Mimecast Ltd MIME 0001734959 FitzGerald Christopher 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 Ordinary Shares 30692 D Ordinary Shares 55000 I By Reporting Person's Spouse 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. Shares held by the Reporting Person's spouse. The Reporting Person disclaims beneficial ownership of these reported securities, and therefore this report shall not be deemed an admission that the Reporting Person is the beneficial owner of such securities for the purpose of Section 16 or for any other purpose. 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 April 2, 2018). /s/ Robert P. Nault, Attorney-in-Fact 2021-10-08