X0306 4 2018-09-07 0 0001644675 Mimecast Ltd MIME 0001734959 FitzGerald Christopher C/O MIMECAST NORTH AMERICA, INC. 191 SPRING STREET LEXINGTON MA 02421 1 0 0 0 Ordinary Shares 2018-09-07 4 S 0 4000 40.9775 D 27821 D Ordinary Shares 2018-09-07 4 S 0 2000 40.9775 D 88000 I By Spouse 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 2018-09-11