If you’re willing to pay for it, Mailbox.org would be my choice. No provider will give that feature away for free (which I’m sure you know). My threat model can tolerate an extra hand via Addy, so I don’t mind them being there.
But no matter who you choose, email just isn’t the best option for true privacy. There will always be some cleartext email somewhere in the process, even if only sometimes. And as somebody once said, “No company is going to break the law for you.”
If you need an extra level of privacy with email specifically, your best option is to self host. That way you control both the server and the database/storage.
You can even get a modern gaming distro based off of it (PikaOS).