Logo
Deploy Now

SaaS Alternative

Fastmail Microsoft 365 Gmail

Categories

Self-Hosted Collaboration Security Communication Email Mail Server CalDAV

Stars

14,303

Forks

899

Watchers

80

Developer links

Last Updated: 08-22-2026 03:02 AM (UTC)

Stalwart

With 14,000 GitHub stars and 81 releases since March 2023, Stalwart is the most protocol-complete open-source mail server available — delivering JMAP, IMAP4rev2, IMAP4rev1, POP3, SMTP, CalDAV, CardDAV, and WebDAV from a single Rust binary that compiles to a memory-safe, zero-garbage-collection executable with predictable latency under load. The SMTP server implements DMARC, DKIMv2, DKIMv1, SPF, and ARC for complete message authentication with automatic DKIM key rotation, while transport security enforces DANE, MTA-STS, and SMTP TLS reporting to prevent downgrade attacks. Built-in spam filtering with statistical classifiers, DNS blocklists, and collaborative reputation databases eliminates the need for external Rspamd or SpamAssassin deployments. Encryption at rest protects stored messages with S/MIME or OpenPGP, and automatic TLS certificate provisioning via ACME supports TLS-ALPN-01, DNS-01, and HTTP-01 challenges without manual certificate management. The ManageSieve server enables server-side email filtering rules, while full-text search indexes message bodies and attachments for instant retrieval. Pluggable storage backends support RocksDB for embedded deployments, PostgreSQL, MySQL, and S3-compatible object storage for distributed architectures. LDAP and SQL-based authentication integrate with existing directory services, and the web administration panel manages domains, accounts, quotas, and DKIM keys. Security audited with memory safety guaranteed by Rust's ownership model. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. AGPL-3.0 licensed.

Stalwart
Stalwart
Stalwart
Stalwart
Stalwart

Benefits

  • Complete Protocol Suite in One Binary
  • JMAP, IMAP4rev2, POP3, SMTP, CalDAV, CardDAV, and WebDAV run from a single Rust executable — eliminating the need to configure, maintain, and update separate Postfix, Dovecot, and Radicale installations.
  • Built-In Spam and Authentication
  • Integrated spam filtering with statistical classifiers and DNS blocklists plus DMARC, DKIMv2, SPF, and ARC authentication eliminate external dependencies on Rspamd, SpamAssassin, or OpenDKIM.
  • Memory-Safe Rust Architecture
  • Written entirely in Rust with zero unsafe code paths, guaranteeing memory safety without garbage collection pauses — delivering predictable latency and eliminating buffer overflow vulnerabilities by design.
  • Automatic TLS Certificate Management
  • ACME integration provisions and renews TLS certificates automatically using TLS-ALPN-01, DNS-01, or HTTP-01 challenges, removing manual certificate renewal workflows and preventing expiration-related outages.

Features

  • JMAP Protocol Support
  • Native JMAP for Mail, Sieve Scripts, WebSocket push, Blob Management, and Quotas provides modern API access with efficient delta synchronization for mobile and web clients.
  • Encryption at Rest
  • S/MIME and OpenPGP encrypt stored messages on disk, protecting mailbox contents even if storage media is compromised or accessed by unauthorized parties.
  • Pluggable Storage Backends
  • RocksDB for embedded single-server deployments, PostgreSQL and MySQL for relational backends, or S3-compatible object storage for horizontally scalable distributed architectures.
  • ManageSieve Server
  • Server-side email filtering via the Sieve scripting language with remote management protocol, enabling users to create rules for sorting, forwarding, and auto-responding without client-side configuration.
  • Web Administration Panel
  • Browser-based management of domains, accounts, quotas, DKIM keys, spam policies, and server configuration without editing TOML files or restarting services.