SPF Classic

Current SPF Protocol Specification: http://www.ietf.org/internet-drafts/draft-schlitt-spf-classic-02.txt

Historical Documents

SPF Classic grew out of RMX and DMP.

RMX

On May 27 2003, Slashdot mentioned Hadmut Danisch's Reverse MX proposal.

Danisch maintains a site at http://www.danisch.de/work/security/antispam.html with available code.

Mike Rubel maintains a page tracking the RMX proposal much as this page tracks the SPF proposal.

DMP

Gordon Fecyk's Designated Mailer Protocol was the inspiration for SPF's original architecture. He maintains a DMP FAQ.