Madmail, a fork of Maddy (see below) which appears to be optimized for use as a Chatmail server. written in Go. last release: 0.12.7, February 2026.
Maddy - "implements all functionality required to run a e-mail server. It replaces Postfix, Dovecot, OpenDKIM, OpenSPF, OpenDMARC and more with one daemon." written in Go. last release: 0.8.2, January 2026.
I didn't find documentation for deploying #Maddy as a #Chatmail relay, but I also only looked for like 2 minutes.