SMTP Phasepre-DATA
CPU Uselow
Memory Usehigh
False Positivesmedium


SPF stands for Sender Policy Framework. It's not specifically an anti-spam measure; rather, it's an attempt to prevent email forgery. Each participating site sets up a little definition of which hosts are allowed to send mail claiming to be from that site. When another site receives mail, it checks the permitted-senders definition for the originating site. If the check fails, the mail is rejected.

Spfmilter implements SPF checking in a sendmail milter. It is still in beta-test stage because both of the SPF libraries it can use are unstable.

SMTP Phasepost-DATA
CPU Uselow
Memory Usemedium
False Positiveslow


Sfcmilter is an add-on for spfmilter that attempts to remedy a deficiency in how SPF is defined. SPF only looks at the sender address in the SMTP transaction - the "envelope address". The sender address in the message itself can be different, and SPF provides no protection against forgeries there. Sfcmilter checks the two sender addresses against each other, and if they don't match then a warning header is added to the message. This warning can serve as a clue to a later phase of the delivery process, such as a Bayesian filter.
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