In a broader sense, the move to create what is essentially a preferred class of e-mail is a major change in the economics of the Internet. Until now, senders and recipients of e-mail -- and, for that matter, Web pages and other information -- each covered their own costs of using the network, with no money changing hands. That model is different from, say, the telephone system, in which the company whose customer places a call pays a fee to the company whose customer receives it.

The prospect of a multitiered Internet has received a lot of attention recently after executives of several large telecommunications companies, including BellSouth and AT& T, suggested that they should be paid not only by the subscribers to their Internet services but also by companies that send large files to those subscribers, including music and video clips. Those files would then be given priority over other data, a change from the Internet's basic architecture which treats all data in the same way.

This Tuesday the Senate Commerce Committee will hold a hearing to consider legislation for what has been called Net neutrality -- effectively banning Internet access companies from giving preferred status to certain providers of content. The concern is that companies that do not pay could find it hard to reach customers or attract new ones, threatening the openness of the Internet.

AOL and its parent, Time Warner, which also owns a large cable system offering high-speed Internet access, have not taken a public stand on the principle of Net neutrality. Neither has Yahoo, which has close relationships with AT& T and Verizon. The issue of e-mail postage has not yet come up in the debate over Net neutrality. 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 the identity of the sender. Goodmail has tested the system with the participation of a few companies, including the American Red Cross and The New York Times.

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, which diverts suspicious messages to a special spam folder. Most of these messages will also not be displayed with their original images and links.

Yahoo will start trying out Goodmail's system in coming months, but it has not decided how paid mail will be differentiated from unpaid, said Brad Garlinghouse, vice president of communications products at Yahoo. Goodmail will charge 1/4 cent to 1 cent per message, with high-volume mailers getting the biggest discounts. It will give more than half of that amount to the e-mail service provider. Goodmail does not envision that individuals will need to pay to have their e-mail delivered to Yahoo or AOL accounts.

When AOL started to explain the details of its plan last month to companies that send a lot of e-mail, many quickly raised objections.