What are SPF records?

Sender Policy Framework (SPF for short) is a protocol that aims to help reduce spam. One hopes to reduce spam by determining whether the sender of a mail message is authorised to send a message.

Within the SPF protocol, an additional domain information field is added to the DNS record. This record specifies which mail servers are authorised to send e-mail on behalf of this domain. If a mail server is not listed here and still sends mail with the domain in question as sender, the mail is considered illegitimate (if the receiving server checks for SPF).

SPF makes a modest contribution to limiting spam. It does help mail servers intercept mail sent by, say, a zombie PC, but not against mail sent by mail servers listed in the relevant domain record. Spammers are therefore increasingly using officially registered domains whose mail servers they also own.