The domainkeys-milter package is an open source implementation of the Domain
Keys sender authentication system proposed by Yahoo!, Now the historical
standard RFC 4870.

This package consists of a library that implements the Domain Keys service
and a milter-based filter application that can plug in to the sendmail MTA to
provide that service to sufficiently recent sendmail MTAs and other MTAs
that support the milter protocol.

An optional asynchronous resolver library is also provided to work around
limitations of the basic BIND resolver which comes installed on most
systems.