Sec Form 4 Filing - Murray Neil @ Mimecast Ltd - 2019-05-06

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Murray Neil 2. Issuer Name and Ticker or Trading Symbol Mimecast Ltd [ MIME] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O MIMECAST NORTH AMERICA, INC., 191 SPRING STREET 3. Date of Earliest Transaction (MM/DD/YY) 05/06/2019 (Street) LEXINGTON, MA02421 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Ordinary Shares 05/06/2019 G V 402 D $ 0 2,281,665 D Ordinary Shares 05/21/2019 M 86,246 A $ 9.21 2,367,911 D Ordinary Shares 05/21/2019 M 25,000 A $ 21.83 2,392,911 D Ordinary Shares 05/21/2019 M 3,250 A $ 34.82 2,396,161 D Ordinary Shares 05/21/2019 S 114,496 D $ 46.6322 ( 1 ) 2,281,665 D Ordinary Shares 05/22/2019 S( 2 ) 25,000 D $ 46.65 ( 3 ) 2,256,665 D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Share Option (Right to Buy) $ 9.21 05/21/2019 M 86,246 ( 4 ) ( 5 ) Ordinary Shares 86,246 $ 0 0 ( 5 ) D Share Option (Right to Buy) $ 21.83 05/21/2019 M 25,000 ( 6 ) ( 5 ) Ordinary Shares 25,000 $ 0 0 ( 5 ) D Share Option (Right to Buy) $ 34.82 05/21/2019 M 3,250 ( 7 ) ( 5 ) Ordinary Shares 3,250 $ 0 0 ( 5 ) D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Murray Neil C/O MIMECAST NORTH AMERICA, INC. 191 SPRING STREET LEXINGTON, MA02421 X Signatures /s/ Robert P. Nault, Attorney-in-Fact 05/23/2019 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $46.50 - $46.935, 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. ( 2 )The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on March 12, 2018. ( 3 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $46.07 - $47.06, 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. ( 4 )Represents shares underlying unexercised share options that were granted on February 1, 2016. The terms of the original grant of 115,000 options provided that twenty-five percent (25%) of the shares vested on February 1, 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. ( 5 )In connection with the Reporting Person's termination of employment with the Issuer on April 5, 2019, all outstanding unvested share options were forfeited by the Reporting Person. ( 6 )Represents shares underlying unexercised share options that were granted on February 1, 2017. The terms of the original grant of 50,000 options provided that 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. ( 7 )Represents shares underlying unexercised share options that were granted on April 2, 2018. The terms of the original grant of 13,000 options provide that twenty-five percent (25%) of the shares vested on April 2, 2019 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.

Remarks: 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).

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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