A place to start looking would be Tutanota. How they measure up in all respects is unclear to me, but they seem to be genuinely trying to be as private as they can.

One that isn't thrown into gmail's spam folder?

I wish I were smart enough to self-host.

When I Degoogled myself I went with Fastmail mostly because (at the time) ProtonMail wanted my left kidney for a sane mail quota.

Haven't regretted the decision since. Spent a while building up email filters and that's about it.

Fastmail is subject to Australian laws though. Australia a passed a troubling anti-encryption law[1], which pretty much means any tech company can be compelled to render assistance.

[1]: https://techcrunch.com/2018/12/05/australia-rushes-its-dange...