Stalwart Mail Server

All-in-one open-source mail and collaboration server written in Rust. Supports IMAP, JMAP, SMTP, CalDAV, CardDAV and WebDAV protocols. Features built-in DMARC, DKIM, SPF, and ARC support, spam filtering, encryption at rest, and clustering support. Community edition is AGPL-3.0 licensed, with optional enterprise license for additional features.