Docker Mailserver

docker-mailserver is a lightweight, production‑ready mail appliance that bundles the full SMTP/IMAP stack with a comprehensive set of anti‑spam, anti‑virus and authentication services—all delivered in a single Docker image. From the developer’s perspective it is essentially a mail‑server as a service that can be versioned, upgraded and scaled with minimal operational overhead. The core philosophy is “no database, only configuration files”, which simplifies CI/CD pipelines and audit trails: every user account, alias or policy is a plain text file that can be checked into Git and diffed across environments.

Key Features

• Full mail stack: Postfix (SMTP), Dovecot (IMAP/POP3), Rspamd, SpamAssassin, ClamAV, OpenDKIM/DKIMARC, Fail2ban, Postscreen/Postgrey.
• LDAP integration: Supports both local file‑based and external LDAP authentication, making it suitable for organizations that already run an LDAP directory.
• Sieve & Quotas: Basic Sieve support for mail filtering and per‑user quota enforcement via Dovecot.
• Extensible filtering: Custom SpamAssassin rules, Rspamd user‑rules and ClamAV signatures can be added through mounted volumes.
• Mail fetching: Optional Fetchmail/Getmail support for retrieving mail from external POP3/IMAP sources.

Technical Stack

The image itself is built from a minimal Alpine Linux base, keeping the attack surface small while providing all required libraries. Configuration is exposed through environment variables and bind‑mounted files, enabling declarative infrastructure-as-code.

Deployment & Infrastructure

docker-mailserver is designed for containerized environments. A single image contains all services; no external database or service is required. For scaling, a typical pattern is to run one instance per domain or per subnet, using Kubernetes StatefulSets or Docker‑Compose with restart: unless-stopped. High‑availability can be achieved by pairing the image behind a load balancer (e.g., HAProxy) with shared mail storage via NFS or a cloud‑managed object store. The image supports TLS termination via Postfix and Dovecot, with automatic Let's Encrypt integration when combined with a reverse‑proxy.

Integration & Extensibility

The project exposes a clean set of environment variables for customizing every component. Advanced users can drop custom Rspamd Lua scripts, SpamAssassin rules or ClamAV virus definitions into dedicated directories. For developers needing programmatic control, the mail server can be queried via IMAP/SMTP clients; Sieve scripts provide a lightweight hook for automated mail routing. The Docker image also ships with a setup.sh script that can be scripted in CI pipelines to generate user accounts, aliases and DKIM keys on the fly.

Developer Experience

• Documentation: The official docs are versioned and hosted on GitHub Pages, with clear sections for “Getting Started”, “Examples” and “Advanced Configuration”. The README contains badges that reflect CI status, pull counts, and documentation availability.
• Community & Support: An active issue tracker on GitHub and a mailing list for discussion. Pull requests are encouraged, and the project follows semantic versioning.
• Configuration Management: All runtime settings are exposed as environment variables; no code changes are required to enable or disable a feature. This makes it trivial to adopt in GitOps workflows.

Use Cases

1. Self‑hosted email for SaaS platforms – Embed a mail server in a Docker Compose stack to provide transactional and user‑mail services without outsourcing.
2. Internal corporate mail – Run on a private network with LDAP authentication, integrating seamlessly with existing directory services.
3. Educational labs – Deploy in a virtual lab to teach students about mail protocols, spam filtering and security hardening.
4. Hybrid cloud – Run locally for sensitive data while exposing a subset of services to the internet via TLS termination.

Advantages

• Zero‑DB, file‑based: Eliminates the need for a separate database service, reducing complexity and deployment cost.
• Container‑friendly: A single image with all dependencies; ideal for Kubernetes or Docker Swarm.
• Open source & permissive license: MIT‑style licensing encourages internal use and commercial deployment.
• Performance & resource footprint: Alpine base + lightweight services keep memory usage below 200 MiB on typical workloads.
• Extensibility: Plug‑in points for custom spam rules, virus definitions and Sieve scripts give developers fine‑grained control.

In summary, docker-mailserver offers a developer‑centric, fully featured mail stack that can be dropped into modern container ecosystems with minimal friction. Its focus on configuration‑driven operation, coupled with a robust set of security and filtering tools, makes it an attractive choice for any project that requires reliable email delivery without the overhead of managing a traditional mail server stack.