MIME 2017 Annual Report

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K (Mark One) ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended March 31, 2018 OR TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 FOR THE TRANSITION PERIOD FROM TO . Commission File Number 001-37637 MIMECAST LIMITED (Exact name of Registrant as specified in its Charter) Bailiwick of Jersey Not Applicable (State or other jurisdiction of incorporation or organization) (I.R.S. Employer Identification No.) CityPoint, One Ropemaker Street, Moorgate London EC2Y 9AW United Kingdom EC2Y 9AW (Address of principal executive offices) (Zip Code) Registrant’s telephone number, including area code: (781) 996-5340 Securities registered pursuant to Section 12(b) of the Act: Ordinary Shares, nominal value $0.012 per share The Nasdaq Stock Market LLC (Title of each class) (Name of each exchange on which registered) Securities registered pursuant to Section 12(g) of the Act: None (Title of class) Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. YES NO Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or 15(d) of the Act. YES NO Indicate by check mark whether the registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. YES NO Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files). YES NO Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K (§229.405) is not contained herein, and will not be contained, to the best of registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K. Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act. Large accelerated filer Accelerated filer Non-accelerated filer (Do not check if a small reporting company) Small reporting company Emerging growth company If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). YES NO The aggregate market value of the voting and non-voting common equity held by non-affiliates of the registrant, based on the closing price of our ordinary shares on the NASDAQ Global Select Market on September 29, 2017, the last business day of the registrant’s second fiscal quarter, was $954,261,949. This calculation does not reflect a determination that certain persons or entities are affiliates of the registrant for any other purpose. The number of registrant’s ordinary shares outstanding as of May 15, 2018 was 58,976,977. DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant’s Definitive Proxy Statement relating to the 2018 Annual General Meeting of Shareholders, scheduled to be held on October 4, 2018, are incorporated by reference into Part III of this Report. The Definitive Proxy Statement will be filed with the Securities and Exchange Commission within 120 days of the registrant’s fiscal year ended March 31, 2018.