GitLab Docker: email configuration


I’m trying to set up sending of emails on GitLab running inside of a Docker container. Searching the web just get’s me instructions on how to set up an SMTP server, but I don’t have one (I don’t want to use my private Gmail account for this).

When installing GitLab directly on my Debian 10 server, everything is running fine, because GitLab finds and uses the “postfix” program which is also installed directly on the server.

I think it’s very great to setup GitLab with just one Docker command, so a) maybe there is a Docker image for an SMTP server, which can be installed that easy as well (and be used with the GitLab Docker container).
The alternative would be to b) get “postfix”, etc. running with(in) Docker GitLab.
How can I achive this or is there another (c)) solution?

Thank’s in advance!