Stalwart

Stalwart replaces the traditional mail server stack, where you'd typically stitch together a separate MTA, message store, spam filter, calendar server, contacts server, and file server, each with its own configuration. It collapses all of that into one platform written in Rust, covering every protocol your clients already speak: JMAP, IMAP4, POP3, SMTP, CalDAV, CardDAV, and WebDAV.

It's built for anyone who wants to self-host email without managing a fragile collection of daemons. That includes small organizations running a single node and hosting providers scaling to millions of mailboxes. The same binary handles both.

Security is default, not optional. Mailboxes at rest can be encrypted with each user's own S/MIME certificate or OpenPGP key, so even an operator with disk access can't read them. Transport security covers DANE, MTA-STS, and TLS reporting. TLS certificates renew automatically over ACME. DKIM keys are generated, rotated, and published to DNS without manual intervention.

Spam and phishing filtering ships inside the product, not as a separate daemon. It includes:

• Statistical classifier with automatic training
• DMARC, DKIM, and SPF sender authentication
• DNSBL checking across IPs, domains, URLs, and hashes
• Phishing protection against homograph attacks and sender spoofing
• LLM-driven message analysis as an optional layer
• Milter and HTTP hooks for SpamAssassin, RSPAMD, and external scanners

Storage and auth are pluggable. Backends include RocksDB, FoundationDB, PostgreSQL, MySQL, SQLite, S3, and Azure Blob. Full-text search works internally or through Meilisearch, ElasticSearch, or OpenSearch. Authentication supports LDAP, OIDC, SQL, or built-in accounts, with 2FA, app passwords, and API keys.

Collaboration is part of the core, not an add-on. Calendars support attendee invitations and free/busy lookup. Contacts sync over CardDAV and JMAP. Files can be stored and shared over WebDAV. One backup, one audit log, one set of access controls covers all of it.

For scale, Stalwart uses peer-to-peer cluster coordination via Zenoh with no external coordinator required, though it also supports Kafka, NATS, and Redis if you prefer. Kubernetes, Docker Swarm, and Apache Mesos orchestration are all supported.