Sorry, I should have been more clear. I'm aware that it's not trivial to implement since they rely so much on the aforementioned OpenPGPjs library and that they're also working on implementing IMAP support. I just meant that the lack of desktop client support killed it for me currently. Once I can plug it into Thunderbird, preferably with an extension of some kind to keep things encrypted, I'll switch to it as my primary email.
Though I am curious as to why you think that's their problem. From what I can tell Protonmail promises that the mail is encrypted on their servers and that accessing it through the official methods (i.e. the website and mobile apps) is also encrypted. While I admire their apparent commitment to extending such promises to the desktop, I'm also surprised they didn't whip up an IMAP interface (which I image would be simpler; send the passphrase to decrypt the mailbox then send the emails like normal) and say "This is for unofficial access, we make no promises".
I'm also iffy on the fact that they don't have an export function. Especially with GhostMail switching to enterprise-only, I am very wary about trusting a webmail service that won't let me back up my emails locally in case they "disappear".
