Sender Policy Framework in a Postfix
This program is based on Matthias Cramer's policyd-spf-fs
(very old project, tested with Debian 6/7 on amd64 and postfix 2.7/2.11)
master.cf
postfix_spfpd unix - n n - - spawn user=nobody argv=/usr/sbin/postfix-policyd-spf-c -w /etc/postfix/filter/spfwhite -d 1