Installing KumoMTA in a Docker container

Quick Start with published Docker Image

Our CI builds the latest version of our image and publishes it to the GitHub Container registry.

You'll need a policy script in order to start kumo. Grab sink.lua, which is a policy that accepts and discards all received mail:

$ curl -O https://raw.githubusercontent.com/kumomta/kumomta/main/sink.lua

The docker image will load the policy file defined by the $KUMO_POLICY environment variable. When we launch the image, we want to mount our sink.lua file into the image and tell it to use it. We recommend using the /config path in the image for that purpose:

$ sudo docker run --rm -p 2025:25 \
    -v .:/config \
    --name kumo-sink \
    --env KUMO_POLICY="/config/sink.lua" \
    ghcr.io/kumomta/kumomta:main

Longer version that shows how to setup docker

Configure Docker

Ensure docker is actually installed in your server instance.

=== "DNF based systems" In Rocky, Alma, and any other DNF package manager system

```bash
sudo dnf config-manager --add-repo=https://download.docker.com/linux/centos/docker-ce.repo
sudo dnf update -y
sudo dnf install -y docker-ce docker-ce-cli containerd.io
sudo systemctl enable docker
```

=== "APT based systems"

In Ubuntu, Debian, and other Debial APT package management systems:

```bash
sudo apt update
sudo apt install -y apt-utils docker.io
sudo snap install docker
```

If you get an error that /etc/rc.d/rc.local is not marked executable then make it executable with sudo chmod +x /etc/rc.d/rc.local

Start Docker

$ sudo systemctl start docker

Check if Docker is running

$ systemctl status docker

Enable Non-Root User Access

After completing Step 3, you can use Docker by prepending each command with sudo. To eliminate the need for administrative access authorization, set up a non-root user access by following the steps below.

Use the usermod command to add the user to the docker system group.

$ sudo usermod -aG docker $USER

Confirm the user is a member of the docker group by typing:

$ id $USER

It is a good idea to restart to make sure it is all set correctly.

Build the KumoMTA container image

You need git to clone the repo:

=== "RPM based systems" bash $ sudo dnf install -y git

=== "APT based systems" bash $ sudo apt install -y git

Then clone the repo and run the image builder script:

$ git clone https://github.com/kumomta/kumomta.git
$ cd kumomta
$ ./docker/kumod/build-docker-image.sh

This should result in something roughly like this:

$ docker image ls kumomta/kumod
REPOSITORY      TAG       IMAGE ID       CREATED         SIZE
kumomta/kumod   latest    bbced15ff4d1   3 minutes ago   116MB

You can then run that image; this invocation mounts the kumo src dir at /config and then the KUMO_POLICY environment variable is used to override the default /config/policy.lua path to use the SMTP sink policy script sink.lua, which will accept and discard all mail:

$ sudo docker run --rm -p 2025:25 \
    -v .:/config \
    --name kumo-sink \
    --env KUMO_POLICY="/config/sink.lua" \
    kumomta/kumod

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