OpenDKIM is a community effort to develop and maintain a C library for producing DKIM-aware applications and an open source milter for providing DKIM service.

The project started from a code fork of version 2.8.3 of the open source dkim-milter package developed and maintained by Sendmail, Inc.

OpenDKIM is an open source implementation of the DKIM (Domain Keys Identified Mail) sender authentication system proposed by the E-mail Signing Technology Group (ESTG), now standardized by the IETF (RFC6376). It also includes implementations of the RFC5617) Vouch By Reference (VBR, RFC5518) proposed standard and the experimental Authorized Third Party Signatures protocol (ATPS, RFC6541).

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.

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

OpenDKIM hosts a data collection facility for sites that wish to volunteer their data. These data are used as feedback to the Internet Engineering Task Force to develop new reputation standards. For more information or a link to the latest report, go here.

Click here to get a copy of our GPG public signing key.


OpenDKIM is a unit of The Trusted Domain Project.


OpenDKIM is proudly sponsored by:

To become an OpenDKIM sponsor, visit The Trusted Domain Project.