To reply, or not to reply? The new legislation Congress approved to stem the flood of unwanted e-mails will require a fundamental change in ways that Internet users respond to overflowing inboxes.

As the deluge of unsolicited pitches offering prescription drugs and cheap loans worsened during the Internet's growth, experts have cautioned computer users against doing what comes naturally: Reply to unwanted e-mails to demand an end to them.

The reason? Unscrupulous spammers (search) deem each such demand a verification that someone actually received their e-mails — and promptly sent dozens more to the same address.

But the "can spam" legislation that Congress approved Monday requires unsolicited e-mails to include a mechanism so recipients could indicate they did not want future mass mailings. Computer users are being asked to ignore years of anti-spam training (search).

"It will require a change in behavior," acknowledged Rep. Heather Wilson, R-N.M., one of the bill's sponsors.

The legislation also will prohibit senders of unsolicited commercial e-mail from disguising their identity by using a false return address or misleading subject line, and it will prohibit senders from harvesting addresses from Web sites.

President Bush has indicated he intends to sign the measure into law. Indeed, the White House revamped its own e-mail system this summer over a flood of so-called spam.

Clogged inboxes have become a leading irritation among Internet users, an increasing business expense for companies and a popular target for Washington interest before an election year.

The House voted without dissent to approve slight changes Senate lawmakers made to the legislation, which would outlaw the shadiest techniques used by the Internet's most prolific e-mailers, who send tens of millions of messages each day.

The bill would supplant tougher anti-spam laws already passed in some states, including a California law that takes effect Jan. 1.

The bill was among the farthest-reaching Internet measures approved during the Bush's term, which has largely continued the Clinton administration's hands-off approach toward regulating America's technology industry. The last such major legislation was a 1998 law banning Web sites from collecting personal information from children under 13.

The anti-spam bill encourages the Federal Trade Commission (search) to create a do-not-spam list of e-mail addresses and includes penalties for spammers of up to five years in prison in rare circumstances. The Senate previously voted 97-0 to approve the bill.

"This is one of the more sweeping Internet regulatory schemes we've seen," said Alan Davidson of the Washington-based Center for Democracy and Technology (search). Although he criticized parts of the anti-spam bill, he said consumer frustration was driving lawmakers. "Most people are going to be glad this bill is heading to the president soon," he said.

Some critics said the bill didn't go far enough to discourage unwanted e-mails. The Coalition Against Unsolicited Commercial E-mails (search) called the congressional effort "really disappointing." The group prefers a law requiring marketers to obtain someone's permission before sending them any e-mails. It said the alternative method of consumers asking marketers not to send them any more messages hasn't worked.

"What Congress is effectively doing is ignoring these laws that haven't worked everywhere else they've tried," said the group's spokesman, John Mozena. "This bill fails the most basic tests for anti-spam legislation; it doesn't tell anybody not to spam."