I don’t think it’s you, it generally is a bad practice to have multiple processes inside a container. It usually defeats most of the isolation, introduces problems with handling zombie processes (therefore you need an init) and restarting tools when they crash (then you need something like supervisord, which I guess this image might use - I didn’t check). Each software adds dependencies, which can conflict (again defeating the idea of containers), and of course CVEs. Then you have a problem with users etc.

So yeah, containers are generally not meant to be used this way. The project might be cool but I would be very uncomfortable running it like this, especially if that’s going to be my primary email, with all the password resetting capabilities etc.