Is free email on its way to extinction?

Four more Internet service providers will start charging banks, e-commerce sites and other large e-mail senders for guaranteed delivery.

In deals expected to be announced Thursday, Goodmail Systems Inc. is expanding its CertifiedEmail program to Comcast Corp., Cox Communications Inc., Time Warner Cable Inc.'s Road Runner and Verizon Communications Inc. Yahoo Inc. and Time Warner Inc.'s AOL became inaugural participants last year.

Individuals, businesses and organizations will be able to continue sending messages for free, but they risk finding those missives caught in increasingly aggressive spam filters.

With Goodmail, a company can pay a quarter of a penny per message to bypass those filters and reach inboxes directly. Recipients see a blue seal verifying that the message is legitimate; senders get confirmations and can resend messages lost in transit.

Non-profit groups can participate, too, at about a tenth of the commercial rates.