I really like ProtonMail for making end-to-end email encryption (relatively) simple.
While ProtonMail (currently) requires another ProtonMail user for bi-directional encrypted email, even emails to users of other systems have some level of encryption. There are some interesting ways of encrypting messages to non-ProtonMail users, and the company says ability to communicate bi-directionally with users with PGP keys is coming.
ProtonMail offers good iOS and Android apps, and a very solid browser interface for use on a desktop or notebook.
Today they have publicly launched ProtonMail Bridge, a small desktop app that allows ProtonMail to easily be used on standard macOS and Windows mail clients, including Apple Mail, Outlook and Thunderbird.
I’ve been using ProtonMail Bridge for the past few weeks with Apple Mail as part of the beta, and it was easy to setup, and has subsequently been very much set and forget.
This is high praise. As far as I am concerned ProtonMail Bridge does exactly what it needs to do - it does its job in the background, and stays out of my way.
While my main personal email is on the excellent Fastmail service, ProtonMail Bridge is making me think that a single email service provider can be my one-stop shop.
Food for thought.
BTW, to learn more about ProtonMail, I suggest you take a look at the following TED talk.