I can recommend Fastmail. No affiliation, just a happy customer. I've used Gmail for several years previously and thought I'd miss it when switching. I didn't.

I also use Fastmail. No affiliations, just a content customer.

I pay for a mobile telephone service, but email is more important to me so my convictions necessitate a paid email service from a dedicated provider with a real support team.

I also own my own domain, primarily because now my email address is short and unambiguous to say over the phone.

Late reply, but I would recommend Posteo [1] because it's flexible and very cheap if you need multiple accounts. I switched to it a year ago to move out of Gmail and other "free" services.

Fastmail is, for my needs of a few mailboxes (each with its own credentials), very expensive - running into few hundred dollars a year!

Another similar and cheap alternative is Mailbox, which allows custom domains to be used.

Both the services allow IMAP, which was very important for me to have local copies of emails if I ever decide to migrate out.

[1]: https://posteo.de

[2]: https://mailbox.org