ARC is a technology proposal, put forward by a consortium of organizations,
intended to allow a chain of message handlers (typically email operators)
to confirm handling by trusted upstream handlers in an attempt to confirm
the valid use of certain identifiers in the message.

OpenARC is an initiative of TDP (The Trusted Domain Project), and is primarily
community effort to develop and maintain an open source library for producing
ARC-aware applications, and a "milter"-based filter for providing ARC service.