Preliminary Proxy Statement

Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))

Definitive Proxy Statement

Definitive Additional Materials

Soliciting Material Pursuant to §240.14a-11(c) or §240.14a-2

No fee required.

Fee computed on table below per Exchange Act Rules 14a-6(i)(4) and 0-11.

Title of each class of securities to which transaction applies:

Aggregate number of securities to which transaction applies:

Per unit price or other underlying value of transaction computed pursuant to Exchange Act Rule 0-11 (Set forth the amount on which the filing fee is calculated and state how it was determined):

Proposed maximum aggregate value of transaction:

Total fee paid:

Fee paid previously with preliminary materials.

Check box if any part of the fee is offset as provided by Exchange Act Rule 0-11(a)(2) and identify the filing for which the offsetting fee was paid previously. Identify the previous filing by registration statement number, or the Form or Schedule and the date of its filing.

Amount Previously Paid:

Form, Schedule or Registration Statement No.:

Filing Party:

Date Filed:

Important Notice Regarding the Availability of Proxy Materials for the Stockholder Meeting

to be held on May 14, 2019, for ServiceSource International, Inc.

This communication presents only an overview of the more complete proxy materials that are available to you on the internet. We encourage you to access and review all of the important information contained in the proxy materials before voting. To view the proxy statement and annual report, go to www.proxydocs.com/srev. To submit your proxy while visiting this site, you will need the 12 digit control number in the box below.

Under United States Securities and Exchange Commission rules, proxy materials do not have to be delivered on paper. Proxy materials can be distributed by making them available on the Internet. We have chosen to use these procedures for our 2019 Annual Meeting and need YOUR participation.

If you want to receive a paper or e-mail copy of the proxy materials, you must request one. There is no charge to you for requesting a copy. In order to receive a paper package in time for this year’s annual meeting, please make this request on or before May 5, 2019.

For a Convenient Way to VIEW Proxy Materials

— and —

VOTE Online go to: www.proxydocs.com/srev

Proxy Materials Available to View or Receive:

1. Proxy Statement   2. Annual Report

Printed materials may be requested by one of the following methods:

INTERNET

www.investorelections.com/srev

TELEPHONE

(866) 648-8133

*E-MAIL

paper@investorelections.com

You must use the 12 digit control number located in the shaded gray box below.

*  If requesting material by e-mail, please send a blank e-mail with the 12 digit control number (located below) in the subject line. No other requests, instructions or other inquiries should be included with your e-mail requesting material.

ACCOUNT NO.

SHARES

Date:    Tuesday, May 14, 2019

Time:    3:00 p.m. (Mountain Time)

Place:   717 17^th Street,  5^th Floor, Denver, Colorado 80202

The purpose of the Annual Meeting is to take action on the following proposals:

Election of Class I Directors

01   Robert G. Ashe

04   Thomas F. Mendoza

07   Richard G. Walker

Vote to authorize the Company’s Board of Directors, in its discretion, to amend the Company’s Certificate of Incorporation to effect a reverse stock split in a ratio of not less than one-for-four and not more than one-for-six.

Advisory vote on compensation of named executive officers for the year ended December 31, 2018.

Ratification of the selection of Ernst & Young LLP as the Company’s Independent Registered Public Accounting Firm for the fiscal year ending December 31, 2019.