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.
had to chime in here because i did my homework on this one :) Cheapest/most space would be inbox.eu - 3 eur a year along with 100gb cloud storage and great privacy, has been around forever in the form inbox.lv. I also use Purelymail but that’s sort of a one man project and better if you need multiple domains. There are also some domain registrars who will offer email free or low cost themselves.