Currently thinking about either Tuta or Mailbox.org, but to be honest, I don’t even know many providers.
Something I do not like is limit on number of addresses with a custom domain. Mailbox is at least a bit reasonable with 50 on Standard, but Proton’s 10 on Mail Plus is disqualifying for me.
Tuta has unlimited number, but doesn’t support PGP.
So I plan to check out whatever you guys use.
I use, and I wrote and run, https://port87.com/.
For custom domains, it supports all the features you can read about on its home page on your own domain.
It takes a bit of adjusting to start using it effectively, because you don’t use the same flow you do with a “normal” email service. I’ve personally got about 150 labels in my account, so I’m definitely a power user (which, I should be, having written it).