OpenDKIM is a community-driven initiative dedicated to creating and maintaining a C library for developing DKIM-aware applications and an open-source milter for DKIM services. This project emerged from a code fork of the open-source dkim-milter package by Sendmail, Inc. OpenDKIM implements the DKIM sender authentication system, along with Vouch By Reference (VBR) and Authorized Third Party Signatures protocol (ATPS) standards.

The package includes a library for DKIM implementation and a milter-based filter application compatible with various MTAs. Additionally, OpenDKIM offers an asynchronous resolver library to overcome BIND resolver limitations. The project hosts a data collection facility to support the development of new reputation standards.

OpenDKIM is part of The Trusted Domain Project and proudly sponsored by various entities. For more information, visit their website to access documentation, services, and ways to support the project