I had a look at the typical ones (fastmail, zoho, protonmail) and recall that in a comment, some 2-3 years ago, someone mentioned a German provider rather directed to geeks. If I remember correctly it is ran by a team of people passionate about mail.
Does that ring a bell?
I just looked up how they make paid services and anonymity go together and they have a page about it here:
Proton is located in Switzerland and Tutanota in Germany. If you need POP3/IMAP then:
https://posteo.de/en/site/features
I am a rather happy fastmail user, with my custom domain. The service is fine but Australia's privacy record is worsening increasingly fast, so at this point I would avoid fastmail if privacy is a concern.
Also https://www.jpberlin.de/ (a political provider), which is the same company (or a sister company?) to mailbox.org