[abrazensunset]

+1, Migadu is simple, reliable, easy, and just works. Cost is low enough it might as well be free. I've only ever had one issue (from incorrectly interpreting documentation) and had an actual human respond and walk me through it.

The only downside to be aware of is the lack of calendar support (technically yes via CalDAV, but that doesn't work for most users--e.g. Calendly won't work).

Edit: the way they handle domains and email aliases has simplified my email life.