Mailu — Docker-Based Self-Hosted Mail Server

Introduction

Mailu packages every component of a production mail server into Docker containers that work together out of the box. Rather than manually configuring Postfix, Dovecot, and a dozen related services, Mailu provides an opinionated, container-native stack with a web-based setup wizard and admin panel. It targets small to medium deployments where simplicity and security matter more than extreme customization.

What Mailu Does

• Runs Postfix (SMTP) and Dovecot (IMAP/POP3) in isolated containers with automatic TLS via Let's Encrypt
• Includes Rspamd for spam filtering with Bayesian learning and optional ClamAV for virus scanning
• Provides Roundcube or Rainloop as webmail clients accessible from the browser
• Offers a web admin panel for managing domains, users, aliases, and relays
• Handles DKIM signing, SPF, DMARC, and autoconfig/autodiscover for email clients

Architecture Overview

Mailu uses Docker Compose to orchestrate a set of microservice containers. The front container (Nginx) handles TLS termination, HTTP routing, and SMTP/IMAP proxying. Behind it, dedicated containers run Postfix, Dovecot, Rspamd, an optional antivirus (ClamAV), the admin interface (Flask-based), and the chosen webmail. A Redis instance coordinates rate limiting and Rspamd state. All persistent data lives in Docker volumes, making backups straightforward.

Self-Hosting & Configuration

• Use the online setup wizard at setup.mailu.io to generate a docker-compose.yml tailored to your domain
• Requires a server with at least 2 GB RAM (4 GB if enabling ClamAV) and ports 25, 143, 443 open
• Configure DNS records (MX, SPF, DKIM, DMARC) as shown in the admin panel's DNS status page
• Environment variables in mailu.env control all settings: domain, TLS mode, message size limits, and features
• Update by pulling new images and running docker compose up -d; data volumes are preserved

Key Features

• Container-native architecture with each service isolated in its own Docker container
• Web-based setup wizard that generates a ready-to-run Compose file for your configuration
• Rspamd integration with auto-learning, greylisting, and DKIM/ARC signing
• Multi-domain support with per-domain quotas, aliases, and catch-all addresses
• Fetchmail integration to pull messages from external accounts into local mailboxes

Comparison with Similar Tools

• Mail-in-a-Box — Single-server Bash installer; simpler but less modular than Mailu's container approach
• Mailcow — Docker-based like Mailu but uses SOGo for groupware; heavier resource footprint
• iRedMail — Script-based installer for bare-metal; more flexible OS support but no container isolation
• Docker Mailserver — Minimal single-container mail setup; lighter but lacks Mailu's admin UI and wizard

FAQ

Q: How much RAM does Mailu need? A: A basic setup runs on 2 GB. Enabling ClamAV antivirus adds roughly 1-2 GB of memory usage.

Q: Can I use Mailu with an existing reverse proxy? A: Yes. Mailu supports running behind Traefik, Nginx, or Caddy by configuring the TLS_FLAVOR and proxy settings in mailu.env.

Q: Does Mailu support two-factor authentication? A: The admin panel supports 2FA for admin accounts. Webmail 2FA depends on the chosen webmail client.

Q: How do I migrate from another mail server? A: Use imapsync or the Fetchmail feature to pull existing messages from your old IMAP server into Mailu mailboxes.

Sources

• https://github.com/Mailu/Mailu
• https://mailu.io/master/