New anti-spam measures will come into force across America on January 1 after President George Bush this week signed the requisite law.

From the new year, commercial emailers must label messages clearly, provide a valid return address and include an 'opt-out' facility. Companies that continue to spam after an 'opt-out' request will face fines of $250 (€202; £142) per email, with a maximum penalty of $2m.

In addition, the legislation gives the Federal Trade Commission powers to set up a US-wide 'do-not-spam' register similar to the 'do-not-call' telemarketing scheme launched this year -- though it does not require the regulator to do so.

Senator Conrad Burns (Republican, Montana), one of the sponsors of the so-called 'Can Spam Act', welcomed Tuesday's presidential signature. "In a country with an ever-increasing reliance on the internet, I am glad to know that today marks a day where Americans will begin to have some muscle against the spammers out there who flood their inboxes each day."

But critics of the scheme -- essentially a compromise between the needs of legitimate marketers and the demands of consumer bodies -- believe lawmakers have given too many concessions to business. They are also unhappy that stricter state laws have been superseded by the national measure.

Now the legislation has been passed, all eyes are on how well it will be policed by the FTC. Marketing trade groups hope vigorous enforcement will deter lawmakers from seeking further measures. "Our fear is that the next round of legislation will be worse," declared Douglas J Wood, general counsel of the Association of National Advertisers.

Data sourced from: New York Times; additional content by WARC staff