If the U.S. Postal Service delivered mail for free, our mailboxes would surely runneth over with more credit card offers, sweepstakes entries and supermarket fliers.
That's why we get so much junk e-mail: It's free to send. So Microsoft Corp. chairman Bill Gates, among others, is suggesting that we start buying "stamps" for e-mail.
Internet analysts worry, though, that turning e-mail into an economic commodity would undermine its value in democratizing communication.
But let's start with the math: At perhaps a penny or less per item, e-mail postage wouldn't significantly dent the pocketbooks of people who send only a few messages a day. Not so for spammers who mail millions at a time.
Though postage proposals have been in limited discussion for years. The details came recently. Instead of paying a penny, the sender would "buy" postage by devoting maybe 10 seconds of computing time to solving a math puzzle. The exercise would serve as proof of the sender's good faith.
Spammers would presumably have to buy many more machines to solve enough puzzles.