I'm trying to enable SPF on my mail server, which runs Postfix 2.5.5 (on Gentoo of course

) There seem to be many different daemons and libraries that implement SPF, but many of them seem to be buggy and/or not actively maintained. Can anyone recommend a particular SPF implementation for Postfix? Ideally, I want a solution that only involves (1) emerging packages that are in Portage and (2) editing the Postfix configuration files. I'd rather not have to apply patches to Postfix or install software that's not in Portage, although I can do so if necessary.
I am
not interested in reasons I shouldn't be using SPF (as I've seen posted on previous threads on this subject).