Sec Form 4 Filing - Bender Alex E.T. @ Mimecast Ltd - 2020-08-11

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 Bender Alex E.T. 2. Issuer Name and Ticker or Trading Symbol Mimecast Ltd [ MIME] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) SVP, Global Marketing (Last) (First) (Middle) C/O MIMECAST NORTH AMERICA, INC., 191 SPRING STREET 3. Date of Earliest Transaction (MM/DD/YY) 08/11/2020 (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 08/11/2020 M 10,000 A $ 10.22 12,118 D Ordinary Shares 08/11/2020 S 10,000 D $ 43.662 ( 1 ) 2,220 ( 2 ) D Restricted Share Units ( 3 ) 2,500 ( 4 ) D Restricted Share Units ( 3 ) 4,500 ( 5 ) D Restricted Share Units ( 3 ) 10,000 ( 6 ) D Restricted Share Units ( 3 ) 12,732 ( 7 ) 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. Transacti on 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) $ 10.22 08/11/2020 M 10,000 ( 8 ) 03/01/2026 Ordinary Shares 10,000 $ 0 11,880 ( 8 ) D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Bender Alex E.T. C/O MIMECAST NORTH AMERICA, INC. 191 SPRING STREET LEXINGTON, MA02421 SVP, Global Marketing Signatures /s/ Robert P. Nault, Attorney-in-Fact 08/12/2020 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 $43.50 - $43.90, 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 )Includes 102 Ordinary Shares issued to the Reporting Person on December 31, 2019 under the Mimecast Limited 2015 Employee Share Purchase Plan. ( 3 )Each restricted share unit represents a contingent right to receive one share of the Issuer's ordinary shares. ( 4 )These restricted share units were granted on April 2, 2018. Twenty-five percent (25%) of the units vested on April 2, 2019, twenty-five percent (25%) of the units vested on April 2, 2020, and the remainder of the units vest on an annual basis over the next two (2) years, provided that the Reporting Person remains an employee of the Issuer on each such vesting date. ( 5 )These restricted share units were granted on April 1, 2019. Twenty-five percent (25%) of the units vested on April 1, 2020 and the remainder of the units vest on an annual basis over the next three (3) years, provided that the Reporting Person remains an employee of the Issuer on each such vesting date. ( 6 )These restricted share units were granted on October 1, 2019. Twenty-five percent (25%) of the units vest on October 1, 2020, and the remainder of the units vest on an annual basis over the next three (3) years, provided that the Reporting Person remains an employee of the Issuer on each such vesting date. ( 7 )These restricted share units were granted on April 1, 2020. Twenty-five percent (25%) of the units vest on April 1, 2021 and the remainder of the units vest on an annual basis over the next three (3) years, provided that the Reporting Person remains an employee of the Issuer on each such vesting date. ( 8 )This option was granted on March 1, 2016. Twenty-five percent (25%) of the shares vested on March 1, 2017 and the remainder of the shares vested on a quarterly basis over the next three (3) years, such that on the date hereof the option is fully vested.

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 January 2, 2020).

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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