Yahoo! just released a draft specification for domain-based e-mail authentication. Essentially, each e-mail has a header with an encrypted hash of the text. In DNS, a special TXT entry with the public key information is stored. The receiving mail servers can use the public key to ensure that the message was generated by the authorized server.
Not a bad idea in concept. I’m still reading the draft, but I’m intrigued by the possibilities.
Comments on Neowin led me to another project, the Sender Policy Framework, which I wasn’t aware of. A whole bunch of cool ideas floating around right now!