Super nice people, when you email them for support they're fast and thorough. Their founders are/have been active on here, and they're currently investing in foss projects by hiring sourcehut.org (Simon Ser and Drew DeVault) to build a new web mail built on modern Go libraries https://git.sr.ht/~migadu/alps.
They've got a list of pros/cons here https://www.migadu.com/procon/
I'll shill them any day because I appreciate their simple goal of creating a good email service with no extra unicord dust, marketing, etc on top, plus their willingness to work on open technologies.
They've got what you'd expect for the price, unlimited domains, great admin dashboard, etc etc. CalDAV and CardDAV come out of beta very soon (end of September iirc).
Because I use rest of their services as well. I understand privacy wise it's not most the optimal solution and I might consider using alternatives in the future.
Not answering the question directly, but since it allows you to use an arbitrary service it might be relevant.
I'm on the free service and have had no issues. I was nervous about it when I started: https://paperstack.com/moving_parts/
I have no affiliation with ImprovMX. I should probably upgrade to the paid service though now I think about it!
No one. I host my email myself.