coexist with basic exim4 server mail

[Waldorf3]

The Debian Bookworm host running this container needs to be able to send standard system related notifications, so I have installed mailutils and exim4. Using "dpkg-reconfigure exim4-config" I set it up with first option, standard internet server, but although I don't expect any incoming mail it insist on at least listening on 127.0.0.1:25. It keeps complaining about this being busy because docker-mailserver is using it. Not a big problem, except it keeps trying, and if it succeeds docker-mailserver will not be able to use it, and that will be a problem.

For now I change the bind line in docker-compose to bind explicitly to the server IP address instead of the usual 25:25, but I am not sure if that will be a problem for docker-mailserver. Maybe some of the subprocesses try to connect to 127.0.0.1:25 - and will then get the host's exim4 server instead.

How to best deal with this?

[polarathene]

Maybe some of the subprocesses try to connect to 127.0.0.1:25 - and will then get the host's exim4 server instead.

• Each container has an IP assigned to it from private address (unless you use host mode networking). This should be unique to the container, no overlap to worry about and you can set an explicit IP within that subnet for reliability if you need to.
• Likewise each container has its own loopback 127.0.0.1, unrelated to the host (unless you use host mode networking).

You should be fine by choosing to restrict the interfaces your container binds ports to. The default is 0.0.0.0 (all) for convenience. If you do not need to reach the container via localhost / 127.0.0.1 on your Docker host, there is no need to bind to it 👍