MAAWG published a revised version of their Sender Best Communication Practices
The Messaging Anti-Abuse Working Group stated in their 2008-06-02 BCP (PDF): "At the very least, senders should incorporate SPF records for their mailing domains".
MAAWG paper about e-mail authentication
In a paper published by the MAAWG in March 2008 Dave Crocker explains the technical background of SMTP e-mail authentication, and the protocols DKIM, SPF, and Sender ID: Trust in Email Begins with Authentication (PDF).