QuickLinks -- Click here to rapidly navigate through this document

Exhibit 32.1

CERTIFICATION OF CHIEF EXECUTIVE OFFICER PURSUANT TO
18 U.S.C. SECTION 1350
AS ADOPTED PURSUANT TO SECTION 906
OF THE SARBANES-OXLEY ACT OF 2002

        I, Mark R. Goldston, certify, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that, to my knowledge:

        (a)   The Quarterly Report on Form 10-Q of United Online, Inc. for the quarter ended June 30, 2010, as filed with the Securities and Exchange Commission fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

        (b)   The information contained in such report fairly presents, in all material respects, the financial condition and results of operations of the Company.

Date: August 6, 2010

/s/ MARK R. GOLDSTON
Mark R. Goldston
Chairman, President and Chief Executive Officer

QuickLinks

Exhibit 32.1

CERTIFICATION OF CHIEF EXECUTIVE OFFICER PURSUANT TO 18 U.S.C. SECTION 1350 AS ADOPTED PURSUANT TO SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002