I would advice to try with mailinabox.email . It is very opinionated, which, for a beginner, is a good thing with mail.

I'd encourage everyone to try this on a tiny droplet or linode with an unimportant domain (don't just migrate your entire companies' exchange into it on a Friday afternoon). It takes you an hour tops, after which you can poke around and see all the moving parts that make a good mailserver tick.

You'll also be contributing to a stronger, more resilient internet, by making it a tiny bit more decentralized.