] DomainKeys is a technology proposal that can bring black
] and white back to this decision process by giving email
] providers a mechanism for verifying both the domain of
] each email sender and the integrity of the messages sent
] (i.e,. that they were not altered during transit). And,
] once the domain can be verified, it can be compared to
] the domain used by the sender in the From: field of the
] message to detect forgeries. If it's a forgery, then it's
] spam or fraud, and it can be dropped without impact to
] the user. If it's not a forgery, then the domain is
] known, and a persistent reputation profile can be
] established for that sending domain that can be tied into
] anti-spam policy systems, shared between service
] providers, and even exposed to the user.

Yahoo! Anti-Spam Resource Center - DomainKeys