What I have found so far:
- posteo looks good, but does not support custom domains
- tutanota can support it though I somewhat doubt their survivability long-term
- proton mail also supports it, but not a huge fan
- zoho: tried it years ago and it was ok, subprocesor list has aws and google on the periphery but not core
- ghandi.net: ?
- fastmail: ?
- kolab: ?
- Mailfence
Are there any others to look at?
I am not looking to self-host.
They all can read your e-mail. Whoever claims the contrary, is lying. Pick the one that offers the best features. A good one which doesn’t cost much is mailbox.org