> The problem is that ProtonMail could violate your privacy by sending you Javascript that gave them your keys and you'd never know about it.

I think we don't agree on how proton mail works. As I understand it, they already have my keys. You can't even give them just a subkey, it only works if you upload a set of PGP keys including the master secret key. What is your understanding of how it works?

As for your other concerns, unless I am conversing only with myself, the attack vector for my data is the entire e-mail ecosystem. Even if I only talk to people who use encrypted email, they are also part of my threat model, even if I don't trust a provider with my keypair. e-mail is simply not secure. It wasn't meant to be secure; security cannot be bolted on top.

What is your threat model and how do other providers or self hosting achieve your desired level of security?