OpenDKIM is an open source implementation of the DKIM sender authentication
system proposed by the E-mail Signing Technology Group (ESTG), now a proposed
standard of the IETF (RFC4871).

The OpenDKIM package consists of a library that implements the DKIM service
and a milter-based filter application that can plug in to any milter-aware
MTA to provide that service to sufficiently recent sendmail MTAs and other
MTAs that support the milter protocol. 

WWW:	http://opendkim.org/