Documentation for ARC is pretty sparse. The instructions for setting it up in Exim (default MTA on Debian systems) can be found here: https://github.com/Exim/e

Documentation for ARC is pretty sparse. The instructions for setting it up in Exim (default MTA on Debian systems) can be found here: https://github.com/Exim/exim/blob/master/doc/doc-txt/experimental-spec.txt#L472 https://github.com/Exim/exim/blob/master/doc/doc-txt/experim... (AFAICT, there is absolutely no mention of ARC in the main Exim documentation: https://exim.org/docs.html https://exim.org/docs.html)