A Colorado man accused of sending hundreds of thousands of spam e-mails has been sentenced to 21 months in prison after pleading guilty to tax evasion and falsifying e-mail headers.

Thirty-five-year-old Edward "Eddie" Davidson of Louisville was also ordered to pay nearly $715,000 to the Internal Revenue Service. He was sentenced Monday and ordered to report to prison authorities in May.

Federal prosecutors say Davidson's operation used false e-mail headers to disguise the sender. Prosecutors say some of the spam was meant to dupe stock investors and manipulate markets.

Authorities say Davidson made at least $3.5 million sending e-mails for nearly 20 companies.