Michael Lucas released a stellar book on the subject not long ago (https://www.tiltedwindmillpress.com/product/ryoms/). It’s pretty thorough, relatively up-to-date, and (like all his stuff) a fun read. It does a great job of demystifying the mechanics. As far as the implementation goes, I’ll put in another vote for Mailcow, which combines all of the components into a very usable docker stack.