Stalwart is an open-source mail and collaboration server written in Rust. It supports JMAP, IMAP, POP3 and SMTP for email, and CalDAV, CardDAV and WebDAV for calendars, contacts and file sharing. Built-in features include DKIM, SPF and DMARC checks, spam and phishing filtering, optional at-rest encryption with S/MIME or OpenPGP, and authentication through LDAP, OIDC or SQL. Storage backends are pluggable, including RocksDB, PostgreSQL, MySQL, SQLite and S3. It runs as a single node or a cluster on Linux, macOS, Windows or Docker.
Stalwart Labs is based in London, United Kingdom, outside the EU and the EEA. The software is dual-licensed under the AGPL-3.0 and a proprietary Stalwart Enterprise License. Because it can be installed on your own infrastructure, a European organisation decides where mail data is stored and who administers it, without depending on a hosted service from the vendor. In that case, jurisdiction depends mainly on the chosen hosting provider.