The US Congress has backed a bill that will hit law-breaking spammers with huge fines and jail sentences.
Everyone gets spam in their inbox
The bill bans spammers from using false return addresses and demands that pornographic spam be labelled as such.
US President George Bush is expected to sign the bill into law by the end of 2003.
But critics of the measure say it will do little to stop and spam and may even encourage some businesses to start sending unwanted mail.
The anti-spam bill cleared its first hurdle in November when it got the backing of the US Senate.
The measure does not go as far as to ban all unsolicited junk mail.
Instead the US is setting up an opt-out scheme that means businesses are free to send mail until people say they do not want it.
The anti-spam measure demands that spammers use subject lines that identify what is inside their messages and bans junk mailers from harvesting e-mail addresses from websites.
It also asks that spam e-mail include a mechanism that lets people tell the sender that they do not want to receive any more messages.
Spammers breaking the new law could face up to five years in jail.
Spam is considered a nuisance by most net users and the junk messages now reportedly makes up 50% of all e-mail.
"For the first time during the internet era, American consumers will have the ability to say no to spam," said Billy Tauzin, House Energy and Commerce Committee Chairman, in a statement.
"What's more, parents will be able to breathe easier knowing that they have the ability to prevent pornographic spam from reaching defenceless, unsuspecting children," he said.
Critics of the bill say it will do nothing to limit the amount of spam being sent because it allows businesses to send spam until told to stop.
Spammers, many of whom operate on the edges of the law, are also unlikely to abide by the restrictions in the bill.
Many spammers are also based outside the US and are beyond the reach of the new law.
Anti-spam activists would have preferred an opt-in scheme in which people who want spam are the only ones that get it.
The bill was branded "really disappointing" by the Coalition Against Unsolicited Commercial E-mails.
"This bill fails the most basic tests for anti-spam legislation; it doesn't tell anybody not to spam," said John Mozena a spokesman for the group.