I have been using Protonmail for about two years now, I think. I was drawn to their service after the Snowden revelations, and loved the fact that they offered full end-to-end, and at rest, encryption. Another thing I love about this company is their transparency. Recently they were under a DDOS attack and instead of brushing it under the rug they communicated in a fully transparent manner. The best part was not one email was compromised. Not one. That is rockstar, this place is rockstar, and if anyone has any sense you should sign up now.
Here is the letter they emailed all of their users.