Iron Mountain (IRM) DEFA14A Additional proxy soliciting materials

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of
the Securities Exchange Act of 1934 (Amendment No.     )

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Filed by a Party other than the Registrant  o
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o	Preliminary Proxy Statement
o	Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))
o	Definitive Proxy Statement
x	Definitive Additional Materials
o	Soliciting Material under §240.14a-12
IRON MOUNTAIN INCORPORATED
(Name of Registrant as Specified In Its Charter)
(Name of Person(s) Filing Proxy Statement, if other than the Registrant)
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*** Exercise Your Right to Vote *** Important Notice Regarding the Availability of Proxy Materials for the Stockholder Meeting to Be Held on June 14, 2018. IRON MOUNTAIN INCORPORATED IRON MOUNTAIN INCORPORATED INVESTOR RELATIONS ONE FEDERAL STREET BOSTON, MA 02110 Meeting Information Meeting Type: Annual Meeting For holders as of: April 17, 2018 Date: June 14, 2018 Time: 9:00 A.M. U.S. Eastern Time (11:00 P.M. Australian Eastern Standard Time on June 14, 2018) Location: Sullivan & Worcester LLP One Post Office Square 21st Floor Boston, MA 02109 You are receiving this communication because you hold shares in the company named above. This is not a ballot. You cannot use this notice to vote these shares. This communication presents only an overview of the more complete proxy materials that are available to you on the Internet. You may view the proxy materials online at www.proxyvote.com or easily request a paper copy (see reverse side). We encourage you to access and review all of the important information contained in the proxy materials before voting. E45350-P05001 See the reverse side of this notice to obtain proxy materials and voting instructions.

Before You Vote How to Access the Proxy Materials Proxy Materials Available to VIEW or RECEIVE: 1. Notice and Proxy Statement2. Annual Report How to View Online: Have the information that is printed in the box marked by the arrow XXXX XXXX XXXX XXXX (located on the following page) and visit: www.proxyvote .com. How to Request and Receive a PAPER or E-MAIL Copy: If you want to receive a paper or e-mail copy of these documents, you must request one. There is NO charge for requesting a copy. Please choose one of the following methods to make your request: 1) BY INTERNET:www.proxyvote.com 2) BY TELEPHONE: 1-800-579-1639 3) BY E-MAIL*:sendmaterial@proxyvote.com * If requesting materials by e-mail, please send a blank e-mail with the information that is printed in the box marked by the arrow XXXX XXXX XXXX XXXX (located on the following page) in the subject line. Requests, instructions and other inquiries sent to this e-mail address will NOT be forwarded to your investment advisor. Please make the request as instructed above on or before May 31, 2018 to facilitate timely delivery. How To Vote Please Choose One of the Following Voting Methods Vote In Person: Many stockholder meetings have attendance requirements including, but not limited to, the possession of an attendance ticket issued by the entity holding the meeting. Please check the meeting materials for any special requirements for meeting attendance. At the meeting, you will need to request a ballot to vote these shares. Vote By Internet: To vote now by Internet, go to www.proxyvote.com. Have the information that is printed in the box marked by the arrow XXXX XXXX XXXX XXXX (located on the following page) available and follow the instructions. E45351-P05001

Voting Items The Board of Directors recommends you vote FOR the following: 1. For the election of eleven (11) directors to the Iron Mountain Incorporated Board of Directors for a one-year term or until their successors are elected and qualified. Nominees: 1a.Jennifer Allerton 1b. Ted R. Antenucci 1c.Pamela M. Arway 1d. Clarke H. Bailey 1e.Kent P. Dauten The Board of Directors recommends you vote FOR proposals 2 and 3. 2. The approval of a non-binding, advisory resolution approving the compensation of our named executive officers as described in the Iron Mountain Incorporated Proxy Statement. 3.The ratification of the selection by the Audit Committee of Deloitte & Touche LLP as Iron Mountain Incorporated's independent registered public accounting firm for the year ending December 31, 2018. NOTE: In their discretion, the proxies are authorized to vote upon such other business as may properly come before the Annual Meeting of Stockholders or any postponement or adjournment thereof. 1f. Paul F. Deninger 1g. Per-Kristian Halvorsen 1h. William L. Meaney 1i.Wendy J. Murdock 1j.Walter C. Rakowich E45352-P05001

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