Exhibit 32.1

CERTIFICATION OF CHIEF EXECUTIVE OFFICER AND CHIEF FINANCIAL OFFICER

PURSUANT TO 18 U.S.C. SECTION 1350,

AS ADOPTED PURSUANT TO SECTION 906

OF THE SARBANES-OXLEY ACT OF 2002

I, Himesh Bhise, certify pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that the Quarterly Report of Synacor, Inc. on Form 10-Q for the quarterly period ended June 30, 2015 fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934 and that the information contained in such Form 10-Q fairly presents, in all material respects, the financial condition and results of operations of Synacor, Inc.

I, William J. Stuart, certify pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that the Quarterly Report of Synacor, Inc. on Form 10-Q for the quarterly period ended June 30, 2015 fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934 and that the information contained in such Form 10-Q fairly presents, in all material respects, the financial condition and results of operations of Synacor, Inc.

A signed original of this written statement required by Section 906 of the Sarbanes-Oxley Act of 2002 has been provided to Synacor, Inc. and will be retained by Synacor, Inc. and furnished to the Securities and Exchange Commission or its staff upon request. This certification “accompanies” the Form 10-Q to which it relates, is not deemed filed with the Securities and Exchange Commission and is not to be incorporated by reference into any filing of the Company under the Securities Act of 1933, as amended, or the Securities Exchange Act of 1934, as amended (whether made before or after the date of the Form 10-Q), irrespective of any general incorporation language contained in such filing.