Postfix policy server for SPF checking

 postfix-policyd-spf-python is a full featured Postfix policy engine for
 SPF checking. It includes a variety of whitelisting mechanisms and policy
 options to enable it to support the widest variety of system requirements.
 It is implemented in pure Python and uses the python-spf module. The SPF
 web site is http://www.openspf.net/. It has been updated to support RFC
 7208.