The dkim-milter package is an open source implementation of the DKIM sender authentication system proposed by the E-mail Signing Technology Group , now a proposed standard of the IETF . DKIM is an amalgamation of the DomainKeys proposal by Yahoo!, Inc. and the Internet Identified Mail proposal by Cisco. This package consists of a library that implements the DKIM 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.