X0206 3 2018-04-01 0 0001644675 Mimecast Ltd MIME 0001010502 NAULT ROBERT P C/O MIMECAST NORTH AMERICA, INC. 191 SPRING STREET LEXINGTON MA 02421 0 1 0 0 Sr. Vice President and GC Share Option (Right to Buy) 19.28 2026-10-03 Ordinary Shares 160000 D Share Option (Right to Buy) 21.83 2027-02-01 Ordinary Shares 25000 D The options were granted on October 3, 2016. Twenty-five percent (25%) of the shares vested on October 3, 2017 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 such vesting date. The options were granted on February 1, 2017. Twenty-five percent (25%) of the shares vested on February 1, 2018 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 such vesting date. Exhibit 24 Power of Attorney (filed herewith) /s/ Lauren Schwarzenholzer, Attorney-in-Fact 2018-04-02