Sender Policy Framework

Sender Policy Framework (SPF) is a simple email-validation system designed to detect email spoofing by providing a mechanism to allow receiving mail exchangers to check that incoming mail from a domain comes from a host authorized by that domain's administrators. The list of authorized sending hosts for a domain is published in the Domain Name System (DNS) records for that domain in the form of a specially formatted TXT record. Email spam and phishing often use forged "from" addresses, so publishing and checking SPF records can be considered anti-spam techniques.

IETF publication RFC 7208 dated April 2014 defines Sender Policy Framework as "proposed standard".

The first public mention of the concept was in 2000 but went mostly unnoticed. No mention was made of the concept again until a first attempt at an SPF-like specification was published in 2002 on the IETF "namedroppers" mailing list by Dana Valerie Lank (née Green), who was unaware of the 2000 mention of the idea. The very next day, Paul Vixie posted his own SPF-like specification on the same list. These posts ignited a lot of interest, and eventually led to the forming of the IETF Anti-Spam Research Group (ASRG) and their mailing list, where the SPF idea was debated among a subscriber base that seemed to grow exponentially day by day. Among the proposals submitted to the ASRG were "Reverse MX" by Hadmut Danisch, and "Designated Mailer Protocol" by Gordon Fecyk.

In June 2003, Meng Weng Wong merged the RMX and DMP specifications and solicited suggestions from other programmers. Over the next six months, a large number of changes were made and a large community had started working on SPF.

Originally SPF stood for Sender Permitted From and was sometimes also called SMTP+SPF, but its name was changed to Sender Policy Framework in February 2004.

In early 2004, the IETF created the MARID working group and tried to use SPF and Microsoft's CallerID proposal as the basis for what is now known as Sender ID.

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