Maddy Mail Server

Maddy is a composable, single-daemon mail server written in Go that implements SMTP (MTA), SMTP/LMTP (MX/Submission) and IMAP access. It includes built-in mail security protocols (DKIM, SPF, DMARC, DANE, MTA-STS), ACME certificate handling and OpenMetrics/Prometheus telemetry, aiming to replace multiple traditional components with a unified configuration and low maintenance surface.

Key Features

• Integrated mail stack: send and receive mail (MTA/MX) and provide mailbox access (IMAP/LMTP) from one daemon; IMAP storage is explicitly marked as beta.
• Built-in security: DKIM signing and verification, SPF checks and DMARC handling plus support for DANE and MTA-STS.
• Flexible storage: filesystem blob store and S3-compatible blob backend; SQL-indexed IMAP storage supports SQLite, PostgreSQL and CockroachDB.
• Observability & ops: OpenMetrics/Prometheus endpoint, ACME-based automatic certificate management, prebuilt tarballs and an official Docker image for deployment.
• Integrations and extensions: designed to interoperate with Dovecot, rspamd, Mailman and external SMTP targets; modular pipeline for checks, signing and routing.
• Developer & build: Go-based codebase using Go modules; release notes document build/tooling requirements for modern Go toolchains.

Use Cases

• Self-hosted mail for individuals or small teams who want an all-in-one MTA+IMAP server with security defaults.
• Consolidating mail delivery and filtering pipelines to reduce the number of separate services (Postfix/Dovecot/OpenDKIM/etc.) to a single configurable daemon.
• Containerized or VPS deployments where observability (Prometheus) and S3/backed storage are desirable.

Limitations and Considerations

• IMAP storage is labelled as "beta" in the project documentation; users requiring mature, feature-rich IMAP implementations are advised to consider pairing maddy with established IMAP servers (e.g., Dovecot) for production IMAP feature parity.
• SQLite-based storage has write-locking characteristics and checkpoint/vacuum considerations that can limit parallel write throughput; larger or high-concurrency deployments should use a server-grade RDBMS (Postgres/CockroachDB).

Maddy provides a compact, security-focused mail server alternative that centralizes mail delivery, storage and protocol handling into a single Go daemon. It is well suited for users who prefer an integrated, modular approach but should be evaluated carefully against workload, IMAP feature needs and storage concurrency requirements.