World's third-most prolific spammer, Scott Richter, agreed to comply with the state laws and let the authorities monitor his business for 3 years.

Microsoft has won a $7 million ($A9.2 million) settlement from Scott Richter, a man once billed as one of the world's third-most prolific spammer. Microsoft said his business sent an estimated 38 million spam messages a year.

In the settlement announced on Tuesday, Richter, who was removed from the Register of Known Spam Operators maintained by the Spamhaus Project, an anti-spam and consumer advocacy group, and his company agreed to comply with federal and state laws, including CAN-SPAM, the federal Controlling the Assault of Non-Solicited Pornography and Marketing Act. He pledged not to send spam to anyone who had not agreed to receive it. He also agreed to let authorities monitor his business, OptInRealBig.com, an internet marketing company based in Westminster, Colorado, for three years to make sure it did not send any illegal spam.

Richter said, "In response to Microsoft's and the New York attorney general's lawsuits, we made significant changes to OptInRealBig.com's emailing practices and have paid a heavy price. I am committed to sending email only to those who have requested it and to complying fully with all federal and state anti-spam laws."

"People engage in spam to make money," Brad Smith, Microsoft's chief counsel, said on Tuesday. "We have now proven that we can take one of the most profitable spammers in the world and separate him from his money. And I think that sends a powerful message to other people who might be tempted to engage in illegal spam."