Washington ? The Senate agreed Wednesday to impose tough new limits on the irritating but lucrative business of e-mailing unwanted sales pitches to millions of people in the United States.

Internet users have complained about mailboxes clogged with offers for prescription drugs, cheap loans, herbal remedies and pornography.

The Senate voted 97-0 to approve the “Can Spam” bill. The measure outlaws the shadiest techniques used by many of the Internet’s most prolific e-mailers, who pump out millions of unsolicited messages daily. Despite the vote, senators cautioned computer users not to expect an immediate end to overflowing inboxes.

“The odds of us defeating spam by legislation alone are extremely low, but that does not mean we should stand idly by and do nothing about it,” said John McCain, R-Ariz., chairman of the Senate Commerce, Science and Transportation Committee.

The bill, sponsored by Sens. Conrad Burns, R-Mont., and Ron Wyden, D-Ore., prohibits senders of unsolicited commercial e-mail from disguising their identity by using a false return address or misleading subject line. The legislation also bans senders from harvesting addresses off Web sites and requires such e-mails to include a mechanism so recipients can indicate they do not want future mass-mailings.

The Bush administration supports the bill, although similar legislation has stalled in the House.

Sens. John Edwards, D-N.C., John Kerry, D-Mass., and Daniel Inouye, D-Hawaii, missed the vote.

Burns said time spent by consumers wading through unwanted messages and the costs to businesses and Internet providers delivering them were “escalating and wide-ranging.” Under the bill, he said, “people will think twice before they send it, and that’s the answer.”

The bill also requires commercial e-mail senders to include their physical address, along with a clear notice that the message is an advertisement or sales pitch.

Violators could be sentenced for up to three years in prison under an amendment by Sens. Orrin Hatch, R-Utah, and Patrick Leahy, D-Vt., leaders of the Judiciary Committee. Their provision explicitly bans spammers from, among other practices, hacking into computers to use as surreptitious relay points to disguise the origin of unwanted e-mails.