[NTLUG:Discuss] verifying DomainKey-Signature: tag with postfix or spamassassin

[Jack Snodgrass]

Yahoo adds a DomainKey-Signature: tag to their mail. Your supposed to be able 
to do a reverse dns lookup of some sort to verify that the maii is authentic. 

Does anyone know how to validate this using postfix or spamassassin? I
did a google
search and didn't see any hits. Seems like something that would be good to 
impament. 

Thanks  - jack