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 *
  AIN ARON J
 2. Date of Event Requiring Statement (Month/Day/Year)
05/24/2018		 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
_____ Officer (give title below) _____ Other (specify below)
5. If Amendment, Date Original Filed(Month/Day/Year)
04/02/2018
(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)
Restricted Share Units (1) 9,259 (2) (3)
D
 

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

Reporting Owners

Reporting Owner Name / Address Relationships
Director 10% Owner Officer Other
AIN ARON J
C/O MIMECAST NORTH AMERICA, INC.
191 SPRING STREET
LEXINGTON, MA 02421		   X      

Signatures

/s/ Robert P. Nault, Attorney in Fact 05/24/2018
**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) Each restricted share unit represents a contingent right to receive one share of the Issuer's ordinary shares.
(2) These restricted share units were granted on April 3, 2017, and 3,086 units vest on April 3, 2018, 3,086 units vest on April 3, 2019, and 3,087 units vest on April 3, 2020, provided that the Reporting Person remains a director of the Issuer on such vesting date.
(3) Due to an administrative error, the number of Restricted Share Units disclosed in this item in the original Form 3 filed on April 2, 2018 was incorrect. The number was overstated in the original by 270 Restricted Share Units.
 
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).

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