CAN-SPAM allowed the DOJ to investigate the defendants for falsifying headers on their e-mail and their domain name registrations, said a DOJ official. That led investigators to find other illegal behavior, she said.

The FTC sees a couple of large benefits from CAN-SPAM, said Lois Greisman, associate director of the FTC's Division of Marketing Practices. The law set the rules for legitimate marketers: Commercial e-mail must have a working opt-out mechanism, must include a valid postal address for the sender, and cannot contain falsified header information or deceptive subject lines, among other rules. CAN-SPAM and FTC rules also require pornographic e-mail to be labeled as such.

CAN-SPAM "set out, in black and white, what the rules of the road are," Greisman said.

In addition, the law gives the FTC the power to seek civil penalties against spammers, authority the agency doesn't have under the FTC Act, the law that prohibits unfair business practices and governs most FTC action. The ValueClick settlement and other large CAN-SPAM settlements should put other spammers on notice, Greisman said.

In November, the FTC announced a US$650,000 settlement with Adteractive, which sent spam promising free gifts such as Xboxes and television sets. And in January, the FTC announced a US$200,000 settlement with Member Source Media, which promised free iPods, gift cards and other products in its e-mail messages.

"Our ability to obtain civil penalties there, I think, will have an effective deterrent impact," Greisman said.

The FTC doesn't need additional spam-fighting tools, she said. CAN-SPAM can be used in conjunction with the FTC's other powers, including the ability to seek asset freezes and injunctions in court, Greisman said. "We can walk into federal court, and with the right set of facts, shut down fraudulent operations," Greisman said. "That's a powerful tool." In addition, spam filters are largely working, even if the amount of spam that's sent isn't going down, she said. "It's less the bombardment than it used to be," she said.

Antispam vendors say CAN-SPAM's had no real impact on the amount of spam being sent, however. In 2003, 35 to 40 per cent of all e-mail was spam, and now that number is 80 to 90 per cent, said Matt Sergeant, senior antispam technologist at MessageLabs. But at the same time, MessageLabs has gone from blocking about 90 per cent of spam to 99 per cent, he added.

But CAN-SPAM has provided some benefits, added Eytan Urbas, vice president of products for Mailshell, another antispam vendor. CAN-SPAM created rules for the "good guys" to follow and allowed the prosecution of the "biggest and worst" spammers, he said. "Spam is growing, but I don't blame CAN-SPAM for that," he added.

Many smaller spammers continue to get away with it, however, Urbas said. "In most cases, [spam] is not the highest priority for law enforcement," he added.

And much of the spam in US inboxes comes from outside the country, he said. "It's hard enough to extradite major criminals, or violent criminals, but there's no extradition for spam," he said.