E-mail is essentially free right now -- but what if you had to pay for each e-mail you sent?

SPAM Tips to cut down on spam: Keep personal and work e-mail separate Delete spam, don't open it Don't post your address on your Web site If you participate in a newsgroup or chat room, use a separate e-mail address Never buy anything advertised on spam Use filtering and blocking software Survey: Penny Per E-Mail?

Double-clicking could cost a pretty penny. But that's why Bill Gates and others say it's a good idea.

The founder of Microsoft argues if people had to buy e-mail "stamps," junk e-mail would be cut back.

Some people are suggesting a charge -- perhaps a penny or less per e-mail. The idea is that while the fee would not add up to much for many people, it would hurt mass mailers who send to millions of people hoping for just a few responses.

Last week, Gates and Microsoft unveiled a new version of the anti-spam idea.

The company suggests people "buy" postage by solving a 10-second math problem. Microsoft says that would be a sign the person is sending e-mail, not a slew of junk mail.

It may seem like the perfect solution to Microsoft, but it could be much harder to convince users that higher math or higher prices are the way to solve e-mail clutter.

Some also say that it would be too complex to put a reliable system in place.