Look, I don't want Google changing this tomorrow because to something tied to and controlled by them because they don't do evel, isn't faster or people like it, but please, don't say it's not hard because you will be misleading people for sure
Edit: to be crystal clear, I agree with parent but don't agree with op
And then there's also the password/username database, that defaults to tying into the Linux pass/user database, so if you want to set up some custom login-data... ugh, I don't even want to think about it.
I set it up once, maintain it here and then, and am keeping it, because dismantling the system is more work than maintaining it presently, but seriously... with the above setup, do it only for educational purposes.
...I'm guessing I spent a week or so properly setting everything up.
...but I'm also willing to try a universal, one-size-fits-all program, if anyone knows anything for Debian?
I then decided to search for a big-monolithic-do-it-all-solution (from a SW-perspective) and the only option I found was Xeams ( https://www.xeams.com/Xeams.htm ) - I didn't find anything open-source. I'm using it (the free variant) since 2017 and it works.
Runs on Java, provides all services (smtp, pop3, imap), has greylisting, has embedded user administration, users can have email-aliases, has a web-admin-UI, 1-click-sw-updates, etc... .
pretty much a set & forget solution. He also writes a new one with all-you-need-to-know extras every time a stable release of debian comes out.