What are your thought on Skiff e-mail provider?
Skiff Mail privacy-first, end-to-end encrypted product home, with Mail, Calendar, Pages, and Drive overview.
They're using Cloudflare which is a bit weird for a "private" service.
IMO if you're starting with your project is understandable, they seem to have a shit ton of money put on it, thought, so that may make it a bit unforgivable, but things can change.