I agree with you. Email is flawed and not appropriate for modern communication.
If you want the messages to be written in letter-like format, then you can write them that way. No need to make it chatty if you don’t want to communicate that way.
Email shares far too much metadata and should be used just for account-updates, account-control (password reset, MFA, and so on), etc.
Otherwise I just push everyone to Signal, since it’s normie-friendly and already using quantum-safe encryption.
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To the OP’s question: yes, I trust Proton. They can’t access my data if they wanted to. They’re a lot better than competing companies.
Check out some of the steps they’ve been taking to improve OpenPGP and go down to “Upcoming improvements” to see their future plans: proton.me/blog/openpgp-crypto-refresh
And, remember, they are more than just an email company: proton.me/blog