relay/docs/DOCKER_INSTALLATION_EN.md

Known issues and limitations

• Requires cgroups v2 configured in the system. Operation with cgroups v1 has not been tested.
• Yes, of course, using systemd inside a container is a hack, and it would be better to split it into several services, but since this is an MVP, it turned out to be easier to do it this way initially than to rewrite the entire deployment system.
• The Docker image is only suitable for amd64. If you need to run it on a different architecture, try modifying the Dockerfile (specifically the part responsible for installing dovecot).

Docker installation

This section provides instructions for installing Chatmail using Docker Compose.

Note: Docker Compose v2 is required (docker compose, not docker-compose) for its support of the cgroup: host option in docker-compose.yaml is only supported by Compose v2. see documentation

apt install docker-ce docker-compose-plugin docker.io- docker-compose-

Preliminary setup

We use chat.example.org as the Chatmail domain in the following steps. Please substitute it with your own domain.

1. Setup the initial DNS records. The following is an example in the familiar BIND zone file format with a TTL of 1 hour (3600 seconds). Please substitute your domain and IP addresses.

    chat.example.com. 3600 IN A 198.51.100.5
    chat.example.com. 3600 IN AAAA 2001:db8::5
    www.chat.example.com. 3600 IN CNAME chat.example.com.
    mta-sts.chat.example.com. 3600 IN CNAME chat.example.com.
   

2. Configure kernel parameters because they cannot be changed inside the container, specifically fs.inotify.max_user_instances and fs.inotify.max_user_watches. Run the following:

echo "fs.inotify.max_user_instances=65536" | sudo tee -a /etc/sysctl.d/99-inotify.conf
echo "fs.inotify.max_user_watches=65536" | sudo tee -a /etc/sysctl.d/99-inotify.conf
sudo sysctl --system

Building the image

Clone the repository and build the Docker image:

git clone https://github.com/chatmail/relay
cd relay
docker compose build chatmail

The build bakes all binaries, Python packages, and the install stage into the image. After building, only docker-compose.yaml and .env are needed to run the container.

TODO: upload the image to a registry, for now, you can upload the image to your server directly with

time docker save chatmail-relay:latest | pigz | ssh chat.example.com 'pigz -d | docker load' # pigz is multithreaded gzip

Running with Docker Compose

1. Copy docker-compose.yaml and docker/example.env into a working directory:

cp docker-compose.yaml /path/to/your/workdir/
cp docker/example.env /path/to/your/workdir/.env

If you are running from the cloned repo directory, just copy the env file:

cp ./docker/example.env .env

2. Configure the .env file. Only MAIL_DOMAIN is required:

• MAIL_DOMAIN – The domain name of the future server. (required)
• CMDEPLOY_STAGES – Deployment stages to run on container start. (default: "configure,activate"). Set to "install,configure,activate" to force a full reinstall.

The container generates a chatmail.ini with defaults from MAIL_DOMAIN on first start. To customize chatmail settings, mount your own chatmail.ini instead (see Customization below).

3. Start the container:

docker compose up -d # start service
docker compose logs -f chatmail # view container logs, press CTRL+C to exit

4. After installation is complete, you can open https://<your_domain_name> in your browser.

Managing the server

Use docker exec to run cmdeploy commands inside the container:

# Show required DNS records
docker exec chatmail /opt/cmdeploy/bin/cmdeploy dns --ssh-host @docker

# Check server status
docker exec chatmail /opt/cmdeploy/bin/cmdeploy status --ssh-host @docker

# Run benchmarks (can also run from any machine with cmdeploy installed)
docker exec chatmail /opt/cmdeploy/bin/cmdeploy bench chat.example.com

Customization

Custom website

You can customize the Chatmail landing page by mounting a directory with your own website source files.

1. Create a directory with your custom website source:

mkdir -p ./custom/www/src
nano ./custom/www/src/index.md

2. In docker-compose.yaml, uncomment or add the website volume mount:

services:
  chatmail:
    volumes:
      ...
      - ./custom/www:/opt/chatmail-www

3. Restart the service:

docker compose down
docker compose up -d

Custom chatmail.ini

There are two configuration modes:

Simple (default): Set MAIL_DOMAIN in .env. The container auto-generates chatmail.ini with defaults on first start. This is sufficient for most deployments.

Advanced: Generate a chatmail.ini, edit it, and mount it into the container. This gives you full control over all chatmail settings.

1. Extract the generated config from a running container:

docker cp chatmail:/etc/chatmail/chatmail.ini ./chatmail.ini

2. Edit chatmail.ini as needed.

3. In docker-compose.yaml, uncomment or add the ini volume mount:

services:
  chatmail:
    volumes:
      ...
      - ./chatmail.ini:/etc/chatmail/chatmail.ini

4. Restart the container. The mounted file is used directly — the container skips generating a new one.

Migrating from a bare-metal install

If you have an existing bare-metal Chatmail installation and want to switch to Docker:

1. Stop all existing services:

systemctl stop postfix dovecot doveauth nginx opendkim unbound acmetool-redirector \
  filtermail filtermail-incoming chatmail-turn iroh-relay chatmail-metadata \
  lastlogin mtail
systemctl disable postfix dovecot doveauth nginx opendkim unbound acmetool-redirector \
  filtermail filtermail-incoming chatmail-turn iroh-relay chatmail-metadata \
  lastlogin mtail

2. Copy your existing chatmail.ini and mount it into the container (see Custom chatmail.ini above):

cp /usr/local/lib/chatmaild/chatmail.ini ./chatmail.ini

3. Copy persistent data into the ./data/ subdirectories:

mkdir -p data/chatmail-dkimkeys data/chatmail-acme data/chatmail

# DKIM keys
cp -a /etc/dkimkeys/* data/chatmail-dkimkeys/

# ACME certificates and account
rsync -a /var/lib/acme/ data/chatmail-acme/

# Mail data
rsync -a /home/ data/chatmail/

Alternatively, you can mount /home/vmail directly by changing the volume in docker-compose.yaml:

- /home/vmail:/home/vmail

The three ./data/ subdirectories cover all persistent state. Everything else is regenerated by the configure and activate stages on container start.

Forcing a full reinstall

The Docker image bakes the install stage (binary downloads, package setup, chatmaild venv) into the image at build time. On container start, only the configure and activate stages run by default.

To force a full reinstall (e.g., after updating the source), either rebuild the image:

docker compose build chatmail
docker compose up -d

Or override the stages at runtime without rebuilding:

CMDEPLOY_STAGES="install,configure,activate" docker compose up -d