Stalwart Mail

Stalwart is an all-in-one mail and collaboration server written in Rust that combines email (IMAP, JMAP, POP3, SMTP), calendars (CalDAV), contacts (CardDAV), and file storage (WebDAV) into a single binary. Where a traditional email setup requires maintaining separate services for each function, Stalwart handles all of it from one process.

The architecture is deliberately modern. Written in Rust for memory safety and performance, it ships with built-in anti-spam tools: a statistical classifier, DNSBL checking, and DMARC/DKIM/SPF validation without needing third-party filters. An optional LLM-based spam analysis layer adds further filtering for environments where that matters.

Clustering is supported natively, which means you can scale horizontally without additional coordination infrastructure. The server is designed to handle millions of mailboxes, making it viable for everything from a personal setup to a commercial hosting operation.

The Community Edition is open-source and free. An Enterprise Edition with additional management features and official support is available for organizations that need it.

Stalwart is newer than established alternatives like Mailcow or Mail-in-a-Box, but it has been gaining traction quickly in the self-host community. Consolidating the email stack into one process that is easy to reason about removes a lot of the operational overhead that has historically made running your own mail server a maintenance burden.