This is a simple milter for SPF checking written in Python.
SPF does email sender validation. For more information about SPF, please see http://www.openspf.org/. SPF is defined in RFC 4408. This spfmilter is the first milter to support all final RFC 4408 requirements.
To use this with sendmail, add the following to sendmail.cf:
O InputMailFilters=%s X%s, S=local:%s
See the sendmail README for libmilter.