The Domain Keys System proposed by Yahoo! is backed by Earthlink & Google. In this system, the eMail server attaches a digital signature with all outgoing eMails which can be verified by the receiving server to validate its authenticity. But other big players AOL & Microsoft have teamed up & have proposed their own system, AOL’s SPF & Microsoft’s SenderID. Both Yahoo! & Microsoft have filed their technologies with Internet Engineering Task Force to make their technologies the global standards.
I think that instead of competing like this, it would be better if both parties teamed up to create a merger of DomainKeys & SenderID to make a more better SPAM prevention system.