Stalwart Mail Server

Stalwart Mail Server is an open-source mail and collaboration server written in Rust. It provides a comprehensive suite of services for handling electronic communication and data synchronization, supporting a wide array of standard protocols for mail, calendars, contacts, and files. The software is deployed as a server application and includes a web-based administration dashboard for managing accounts, domains, and system configurations.

It is designed for various scales of deployment, from small individual setups to large clusters using container orchestration tools like Kubernetes, Apache Mesos, or Docker Swarm. The server handles the full lifecycle of email delivery, from inbound throttling and filtering to outbound delivery with distributed virtual queues and priority routing.

Key features

• Support for JMAP, IMAP4, POP3, and SMTP protocols
• Collaboration tools via CalDAV, CardDAV, and WebDAV
• Built-in spam and phishing filters with LLM-driven analysis and DNSBL checking
• Message authentication using DMARC, DKIM, SPF, and ARC
• Pluggable storage backends including PostgreSQL, MySQL, SQLite, and S3-compatible storage
• Automatic TLS certificate provisioning via ACME
• Multi-tenancy support with domain and tenant isolation
• Authentication integration with OpenID Connect, LDAP, and OAuth 2.0
• Full-text search capabilities across 17 languages

The architecture emphasizes memory safety and scalability, utilizing peer-to-peer cluster coordination or integrations with Kafka, NATS, or Redis for high availability. It offers flexible data management through sharded blob storage and read replicas to maintain low latency. The system includes a self-service portal for password resets and encryption-at-rest key management using S/MIME or OpenPGP. It is intended for administrators who require a standards-compliant communication platform with integrated security auditing and observability via OpenTelemetry and Prometheus.

Stalwart Mail Server serves as a complete, self-hosted solution for organizations needing a unified mail and collaboration infrastructure.