SPF Policy Daemon for Postfix
policyd-spf-fs is a policy daemon for Postfix to check SPF records (RFC 4408). It uses the libspf2 library and is implemented in C. Currently it is only tested on Debian GNU/Linux, but it should compile on most *NIX derivatives with a recent gcc.
It was written because no recent policy daemon existed that worked reliably enough for a high-load mail system and supported IPv6 SPF entries.
For more information about SPF and implementations for other MTAs, have a look at the OpenSPF site.