Ryan Samuel Pitylak, a student at the University of Texas, and his associate Mark Stephen Trotter, were accused of sending up to 25 million spam emails a day.
Pitylak will sell his $430,000 (£228,800) house, luxury car and other assets to help pay the fine and legal bills.
But Pitylak has now surprised some in the industry by announcing plans to set up an anti-spam company.
"I am pleased to announce that I am now part of the anti-spam community, having started an internet security company," he said.
"Over time I have come to see how I was wrong to think of spam as just a game of cat and mouse with corporate email administrators. I now understand why so much effort is put into stopping it."
However, Graham Cluley, senior technology consultant at Sophos, questioned whether companies would want to take advantage of Pitylak's experience.
"Spammers like Pitylak have shown themselves to be prepared to break the law in their eagerness to pump out unwanted marketing messages," he said.
"Some companies may feel uncomfortable about working with someone who has shown a history of behaving unethically, without caring about the consequences for other internet users."
Cluley added that the authorities had to make it clear that spamming is unacceptable, and that legitimate rewards cannot be gained on the back of unsavoury activities.
Spam emails sent by Pitylak contravened the American CAN-SPAM Act, which forbids email marketers from using bogus names or failing to give recipients a legitimate way to unsubscribe.
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