I recently moved to ProtonMail and I am very happy about it.

Protonmail seems fine, but their prices are way too high. Comparable service charge a tenth of what they ask.

Also they don't support open protocols, last I checked -- specifically POP3, imap, and SMTP. I still use Protonmail, but it's a consideration to factor in.

We do support IMAP/SMTP via the ProtonMail Bridge.

It's a proprietary binary, and I need to email you for the Linux version (although I'm sure the latter will change once it's more stable).

My understanding is also that it's not intended to be exposed on the internet, which leaves my Blackberry a bit out of luck.

Not to diminish your work, but the ProtonMail Bridge solution doesn't really meet my needs in the same way native POP3 support would.

Take a look at ProtonMail.com