Implementation of SPF in Postfix is a very simple task. First step is a download and install of the postfix-policyd-spf (http://www.openspf.org/Software). There also exist an easy to install packages for the most popular Linux distributions. There is a version both in Python and Perl (postfix-policyd-spf-python or postfix-policyd-spf-perl).
Next you have to add the following lines to the master.cf:
spfpolicyd unix - n n - 200 spawn user=nobody argv=/usr/bin/policyd-spf
And to main.cf file:
smtpd_recipient_restrictions = ... check_policy_service unix:private/spfpolicyd, ...
Then restart the Postfix and send a test email. You should see the similar lines in your mail.log file.
policyd-spf: None; identity=helo; client-ip=192.x.x.x; helo=remoteserver.net; firstname.lastname@example.org; email@example.com policyd-spf: None; identity=mailfrom; client-ip=192.x.x.x; helo=remoteserver.net; firstname.lastname@example.org; email@example.com
IP addresses and email addresses has been changed.
For most applications policyd-spf requires no configuration file changes.