Sounds useful

I second Diane's experience. The thing is that the amount of stuff to learn & get right is a lot, that's true, but once it's been set up it's definitely _not_ a full-time job per 50 mailboxes. I've been running my own mail server both for myself & my company of ~50 people for years now, and the amount of time I have to spend with mail-server related issues averages to single-digit minutes per day, if that.

The huge timesink is, unfortunately, the very start where you have to learn about everything & get everything right, otherwise you'll fight issues such as non-delivery, landing on anti-spam blocklists etc. for a long time. The initial barrier is huge, the ongoing maintenance very low.