DomainKeys: Proving and Protecting Email Sender Identity
I just discovered this by examinating a message comes from yahoo to my mail serverNot so sure hwo it differenciate from SPF, but according to
http://antispam.yahoo.com/domainkeys
http://domainkeys.sourceforge.net/
The entire message needs to be examined in order to authenticate the domainkeys from DNS
Here is the Sendmail plugin
http://sendmail.net/dk-milter/
To all mail servers admin: Are you tired yet?