Wired News reports:

Under Yahoo's new architecture, a system sending an e-mail message would embed a secure, private key in a message header. The receiving system would check the Internet's Domain Name System for the public key registered to the sending domain.

If the public key is able to decrypt the private key embedded in the message, then the e-mail is considered authentic and can be delivered. If not, then the message is assumed not to be an authentic one from the sender and is blocked.

"One of the core problems with spam is we don't know, Yahoo doesn't know, the user doesn't know ... if it really came from the party who it says it came from," Brad Garlinghouse, vice president for communication products at Yahoo, told Reuters. "What we're proposing here is to re-engineer the way the Internet works with regard to the authentication of e-mail."