Just the presidential signature is now required for America's anti-spam legislation to become law.

The House of Representatives this week approved the Senate's final changes to the bill and sent it to the White House. The measure is due to take effect on January 1.

Under the forthcoming law, 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 would face fines of $250 (€205; £144) 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.

The law will supersede all state anti-spam measures, creating a single national email marketing code.

Data sourced from: The Wall Street Journal Online; additional content by WARC staff