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.


There’s also IP address reputation, IP warm-up (not necessary for personal servers, though), missing things like list-unsubscribe (again, not necessary for personal servers), and of course a touch of “this message looks like other messages that users have marked as spam” on an email from your own server with a message to yourself. There’s so much more than just a Bayesian spam filter in Gmail’s black box.
Also if your ISP puts your IP on the PBL. They also don’t like it if your reverse lookup doesn’t match your domain. I was able to send from my IP for a while and then Google stopped delivering my mail with the PBL given as the reason. Other destinations may be less picky but Google has a lot of requirements some of which are out of your hand unless you have a static IP.
I think all email services should be required to list their delivery requirements publicly.
I just ended up using the free plan of a relay that allows more on their free plan than I’ll ever used in a month.