For those considering Proton Mail: There is one great benefit or disadvantage, depending on how you see it. As all traffic is encrypted, Proton Mail does not support standard IMAP or POP3. It’s therefore best used with the official Proton Mail app rather than third party apps. On desktop, you can use your favourite email client (Thunderbird et al) only if you install a “bridge” which decrypts incoming emails before forwarding them to the client: this bridge is, in turn, only available to paying subscribers.

That said, it’s a great service, and the fact that they have a viable business model which doesn’t depend on selling out their users might be a good thing.