Ownership Submission
FORM 3
 UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES

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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(Print or Type Responses)
1. Name and Address of Reporting Person *
  Bauer Peter
 2. Date of Event Requiring Statement (Month/Day/Year)
04/01/2018		 3. Issuer Name and Ticker or Trading Symbol
Mimecast Ltd [MIME]
(Last)
(First)
(Middle)
C/O MIMECAST NORTH AMERICA, INC., 191 SPRING STREET		 4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
__X__ Director _____ 10% Owner
__X__ Officer (give title below) _____ Other (specify below)
Chief Executive Officer
 5. If Amendment, Date Original Filed(Month/Day/Year)
(Street)

LEXINGTON, MA 02421		 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 Beneficially Owned
1.Title of Security
(Instr. 4)		 2. Amount of Securities Beneficially Owned
(Instr. 4)		 3. Ownership Form: Direct (D) or Indirect (I)
(Instr. 5)		 4. Nature of Indirect Beneficial Ownership
(Instr. 5)
Ordinary Shares 45,000
D
 
Ordinary Shares 2,026,876
I
By Declaration of Trust of Peter Bauer (1)
Ordinary Shares 2,317,500
I
By Rock Trustees Limited (2)

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly. SEC 1473 (7-02)
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Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security
(Instr. 4)		 2. Date Exercisable and Expiration Date
(Month/Day/Year)		 3. Title and Amount of Securities Underlying Derivative Security
(Instr. 4)		 4. Conversion or Exercise Price of Derivative Security 5. Ownership Form of Derivative Security: Direct (D) or Indirect (I)
(Instr. 5)		 6. Nature of Indirect Beneficial Ownership
(Instr. 5)
Date Exercisable Expiration Date Title Amount or Number of Shares
Share Option (Right to Buy)   (3) 02/01/2026 Ordinary Shares 150,000 $ 9.21 D  
Share Option (Right to Buy)   (4) 02/01/2017 Ordinary Shares 75,000 $ 21.83 D  

Reporting Owners

Reporting Owner Name / Address Relationships
Director 10% Owner Officer Other
Bauer Peter
C/O MIMECAST NORTH AMERICA, INC.
191 SPRING STREET
LEXINGTON, MA 02421		   X     Chief Executive Officer  

Signatures

/s/ Lauren Schwarzenholzer, Attorney-in-Fact 04/02/2018
**Signature of Reporting Person Date

Explanation of Responses:

* If the form is filed by more than one reporting person, see Instruction 5(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).
(1) These shares are held by the Declaration of Trust of Peter Bauer. The Reporting Person is a beneficiary, and the sole trustee of, the Declaration of Trust of Peter Bauer.
(2) These shares are held by Rock Trustees Limited as trustees of the Butterworth Trust (the "Butterworth Trust"), of which the Reporting Person is a beneficiary. As trustee of the Butterworth Trust, Rock Trustees Limited exercises dispositive power over the shares held therein. The Reporting Person disclaims Section 16 beneficial ownership of the shares held by the Butterworth Trust, except to the extent, if any, of his pecuniary interest therein.
(3) The options were granted on February 1, 2016. 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.
(4) 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.
 
Remarks:
Exhibit 24 Power of Attorney (filed herewith)

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