policyd-spf-fs is a policy daemon for postfix to check spf records (RCF 4408). It uses the libspf2 library and is implemented in C. Currently is is only tested to run under Debian/GNU Linux, but should be compilable under most *NIX derivates with a recent gcc.
It was written because there did not exist any recent policy daemon which worked reliably enough for a high load mail system and suports ip6 spf entries.
For more information about SPF and implentations for other MTA's please have a look at the official OpenSPF site.