OpenDKIM

OpenDKIM is a powerful software that has been developed by a community consisting of experts in this particular field. Its main purpose is to create and maintain a C library that produces DKIM-aware applications, as well as an open source milter that provides DKIM service. The project was initiated as a code fork of the open source dkim-milter package developed by Sendmail, Inc., with version 2.8.3 as the starting point.

OpenDKIM is an open source implementation of the DKIM sender authentication system created by the E-mail Signing Technology Group (ESTG). This system is now a proposed standard by the Internet Engineering Task Force (IETF) under RFC4871. This software package is designed to work with any milter-aware MTA and can plug in to any suitable MTA to allow users to provide this service to sendmail MTAs and other MTAs that support the milter protocol.

The OpenDKIM package comprises of two main components —a library that performs the DKIM service and a milter-based filter application. The latter is capable of plugging seamlessly into any milter-aware MTA. The software also comes with an optional asynchronous resolver library that works around the limitations of the basic BIND resolver. This feature is particularly useful for users who are working with systems where the basic BIND resolver has been installed.

Overall, OpenDKIM is a highly effective software solution that comes with excellent features for those looking to integrate auxiliary applications with their existing MTA infrastructure.