while migrating to a new server and setting everything up on docker, i found this poste.io mail server. https://www.poste.io
i selected the free version, but if i was working with a company that wanted to migrate to this i would probably go with PRO+
after getting the server to work i made a docker-compose file to make things easy on me. the .env holds the settings to change. as i already have services using port 80, i added a second IP address to the network card and specifying that IP in the .env will tell the setup to use it.