Soon companies will have to buy the electronic equivalent of a postage stamp if they want to be certain that their e-mail will be delivered to many of their customers.
America Online and Yahoo, two of the world's largest providers of e-mail accounts, are about to start using a system that gives preferential treatment to messages from companies that pay from 1/4 cent to a penny each to have them delivered.
The Internet companies say that this will help them identify legitimate mail and cut down on junk e-mail, identity-theft scams and other scourges that plague users of their services.
The two companies also stand to earn millions of dollars a year from the system if it is widely adopted.
AOL and Yahoo will still accept e-mail from senders who have not paid, but the paid messages will be given special treatment. On AOL, for example, they will go straight to users' main mailboxes and will not have to pass through spam filters that could divert them to a special bulk e-mail box or strip them of images and Web links.
Critics of the plan say that the companies risk alienating users and companies that send e-mail. The system will apply not only to mass mailings but also to individual messages like order confirmations from online stores and customized low-fare notices from airlines.
"AOL users will become dissatisfied when they don't receive the e-mail that they want, and when they complain to the senders, they'll be told, 'It's AOL's fault,'" said Richi Jennings, an analyst at Ferris Research, which specializes in e-mail.
As for companies that send e-mail, "some will pay, but others will object to being held to ransom," she said. "A big danger is that one of them will be big enough to encourage AOL users to use a different e-mail service."
In the next two months, AOL will start accepting e-mail processed by Goodmail Systems, a company in Mountain View, Calif., that will collect the electronic postage and verify senders' identities.
Paying senders will be assured that their messages will be delivered to AOL users' main in-boxes and marked as "AOL Certified E-Mail." Unpaid messages will be subject to AOL's spam-filtering process.
Yahoo will start testing Goodmail's system in coming months.