Chatmail relays provide en end-to-end encrypted chat over SMTP with metadata minimization. This is used by Delta.chat to enable reliable and secure instant messaging.
Implementing this would make Stalwart collaboration services embraces next-generation safe instant messaging and circle the feature set of modern collaboration – email, file sharing, tasks, calendar, and chat.
At the time of writing, the existing implementation involves: Postfix, Dovecot, filtermail, Nginx, acmetool, OpenDKIM, mtail, Iroh relay, TURN, and chatmaild services.
Most of these features are already implemented in Stalwart, so it should be a minimal addition to Stalwart to integrate the chat features, and become a solid Delta.chat service provider alternative, reinforcing both environments.
Moreover, both Stalwart and Delta.chat are NGI funding reciptients, and share the license (AGPL), coding language (Rust), and support forum software (Discourse 
). This all looks like a low-hanging fruit for a big gain.
