Not sure i really like this approach too much...
"A system that backers claim will eliminate e-mail spam is about to be deployed by a major Internet service provider, giving a boost to an emerging technology that if widely adopted would change how people communicate online.
Earthlink will roll out test versions of the system for its 5 million subscribers this month. Known as "challenge-response" technology, the system thwarts the ability of spammers to reach their intended audience with millions of automatically generated e-mails. When someone sends an e-mail to a challenge-response user, he or she gets an e-mail back asking to verify that the sender is a live person. Once the sender does that by replicating a word or picture displayed on the screen, the original e-mail is allowed through. The system automatically recognizes future e-mails from the same sender, so the verification needs only to be performed once. Without the verification, the e-mail is not delivered.
Some experts see problems with the technology and doubt that consumers will warm to a process that adds another step to e-mail delivery. The technology is available from a handful of small vendors for a fee, but the customer base is small. "