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Maintain a Mailu server

Upgrading the mail server

First check upstream for changes in the docker-compose.yml or in the .env files. Also, check CHANGELOG.md for changes that you might not want to include.

Update your .env file to reflect the version that you wish to install (if you are running stable or latest, you may skip this and proceed), then simply pull the latest images and recreate the containers :

docker compose pull
docker compose down
docker compose up -d

Monitoring the mail server

Logs are managed by Docker directly. You can easily read your logs using:

docker compose logs

Docker is able to forward logs to multiple log engines. Read the following documentation for details: https://docs.docker.com/engine/admin/logging/overview/.

Managing of external Let’s Encrypt certificates

When you are not using the embedded letsencrypt option from Mailu, you cannot make use of it’s symlink functionality in the letsencrypt/live directory. You should take care that after every renewal new certificates are copied to /mailu/certs and the nginx process in the front container is reloaded.

In the case of certbot you could write a script to be executed as deploy hook. Example:

#!/bin/sh
cp /etc/letsencrypt/live/domain.com/privkey.pem /mailu/certs/key.pem || exit 1
cp /etc/letsencrypt/live/domain.com/fullchain.pem /mailu/certs/cert.pem || exit 1
docker exec mailu_front_1 nginx -s reload
docker exec mailu_front_1 doveadm reload

And the certbot command you will use in crontab would look something like:

52 0,12 * * * root /usr/bin/certbot renew --deploy-hook /path/to/script.sh

Migrating an instance

The SMTP protocol has an embedded retry mechanism and multiple MX that can serve a single domain, so that most migration processes or maintenance processes do not require any specific care.

Mailu relies heavily on files for storing everything, which helps the migration process, that can be performed based on file synchronization.

The suggested migration process consists of setting up a new backup server that drops incoming emails (Mailu not started), synchronizing both servers, stopping the main server and launching the backup server. Then, the backup server is switched as a main MX and the old server is deleted.

  1. Prepare your new server, copy your docker-compose.yml, .env and basic configuration files to the server, so that it is ready to start configuration Mailu, do not start Mailu

  2. Setup your DNS so that the backup server is an additional, deprioritized MX for the domain; this can be complex if you serve many domains, in which case you can simply accept that some remote MX will retry for a couple of minutes, skip this step

  3. While your DNS TTL expires and your modification propagates, start rsyncing your Mailu directory (data, dkim, mail, etc.) to the new server, repeat until there are only a couple files synchronized

  4. Stop Mailu on the old server and run a final rsync while no process is writing to the files

  5. Start Mailu on the new server, and production should be back to normal

  6. Set your new server as the main MX for your domains, if you did not set an additional MX, make sure you still change the A and AAAA record for your MX name.