Thoughts on Skiff compared to ProtonMail?
Skiff – Privacy-first end-to-end encrypted email
Comments ( https://news.ycombinator.com/item?id=37229270 )
Discussion
Email aren't meant for E2E if the receiver doesn't have same email provider it will just send it over plain text.
So just use PGP with any provider you want :)
Encryption at rest is important. Otherwise your provider can read all stored emails.
Imo with email just selfhost so that they don't read your emails orchange prices or just shutdown the service and then you'll have to search another provider. Also use pgp if you want more privacy.