Docker compose requirements

Hardware considerations

You should make sure that your hardware (virtual or physical) is compatible with the latest Linux kernel. The minimal required memory and swap are:

When using antivirus (clamav):
- 3GB of memory
- 1GB of swap
When not using antivirus (clamav):
- 1GB of memory
- 1GB of swap

Pick a distribution

The mail server runs as a set of Docker containers, so it is almost operating system agnostic.

Because most of our tests run on Debian stable, we recommend one of these for the base system. Mailu should however be able to run on any of the officially supported distributions.

For the purpose of this guide, all examples are based on Debian stable. The differences with other system will however hardly be noticeable.

Install the distribution

First, install Debian stable from the netinstall CD image. When installing, make sure that you either:

setup a root ext4 partition,

or setup a root btrfs partition,

or leave enough unpartitioned space for a dedicated ext4 or btrfs partition.

If you chose to create a dedicated partition, simply mount it to /var/lib/docker. You could also create a separate partition (ext4 is a sane default) and mount it to /mailu for storing e-mail data.

Docker supports AUFS over ext4 and btrfs as stable storage drivers. Other filesystems are supported such as OverlayFS. If you know what you are doing, you should go for it.

Mailu uses Docker port forwarding from the host to make services available to external users. First, your host should have a public IP address configured (see /etc/network/interfaces) or your router should forward connections to its internal IP address. Due to spam problems and reputation services, it is highly recommended that you use a dedicated IP address for your mail server and that you have a dedicated hostname with forward and reverse DNS entries for this IP address.

Also, your host must not listen on ports 25, 80, 110, 143, 443, 465, 587, 993, 995 nor 4190 as these are used by Mailu services. Therefore, you should disable or uninstall any program that is listening on these ports (or have them listen on a different port), and make sure that these ports are open in your firewall if you have one. For instance, on a default Debian install:

apt-get autoremove --purge exim4 exim4-base

Finally, Docker relies heavily on iptables for port forwarding. You should use iptables-persistent (or any equivalent tool on other systems) for managing persistent rules. If you were brave enough to switch to nftables, you will have to rollback until official support is released by Docker or setup your own rulesets.

Install Docker

Mailu relies on some of the latest Docker features. Therefore, you should install Docker from the official repositories instead of your distribution ones.

The Docker website is full of detailed instructions about setting up a proper Docker install. Default configuration should be suited for Mailu.

Additionally, you must install docker compose v2 by following the instructions from the Docker website if you plan on using the Compose flavor. Compose is a management tool for Docker, especially suited for multiple containers systems like Mailu.

Once everything is setup, you should be able to run the following commands (exact version numbers do not matter):

$ docker version
  Client: Docker Engine - Community
   Version:           20.10.22
   API version:       1.41
   Go version:        go1.18.9
   Git commit:        3a2c30b
   Built:             Thu Dec 15 22:27:03 2022
   OS/Arch:           linux/arm64
   Context:           default
   Experimental:      true

  Server: Docker Engine - Community
   Engine:
    Version:          20.10.22
    API version:      1.41 (minimum version 1.12)
    Go version:       go1.18.9
    Git commit:       42c8b31
    Built:            Thu Dec 15 22:25:25 2022
    OS/Arch:          linux/arm64
    Experimental:     false
   containerd:
    Version:          1.6.14
    GitCommit:        9ba4b250366a5ddde94bb7c9d1def331423aa323
   runc:
    Version:          1.1.4
    GitCommit:        v1.1.4-0-g5fd4c4d
   docker-init:
    Version:          0.19.0
    GitCommit:        de40ad0

$ docker compose version
  Docker Compose version v2.14.1