X0306 4 2019-09-19 0 0001644675 Mimecast Ltd MIME 0001676306 Murray Neil C/O MIMECAST NORTH AMERICA, INC. 191 SPRING STREET LEXINGTON MA 02421 1 0 0 0 Ordinary Shares 2019-09-19 4 S 0 35000 38.32 D 1766665 D The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on February 15, 2019. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $38.00 - $38.64, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. 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 2019-09-20