EXHIBIT 32.1

CERTIFICATION PURSUANT TO

18 U.S.C. SECTION 1350,

AS ADOPTED PURSUANT TO

SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Annual Report on Form 10-K of CMGI, Inc. (the “Company”) for the fiscal year ended July 31, 2005 as filed with the Securities and Exchange Commission on the date hereof (the “Report”), the undersigned, Joseph C. Lawler, President and Chief Executive Officer of the Company, hereby certifies, pursuant to 18 U.S.C. § 1350, as adopted pursuant to § 906 of the Sarbanes-Oxley Act of 2002, that to my knowledge:

(1) The Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

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

Date: October 14, 2005	By:	/s/ Joseph C. Lawler
		Joseph C. Lawler
		President and Chief Executive Officer