I think in the end most computer users will sacrifice a bit of security for convenience. PGP signature and encryption for email will most likely never take off. Encrypted chat services like Signal seems to have done much better, likely because of how convenient they are to use.
This stores the private key as a password-encrypted file in a specified location on the IMAP server. It already has multiple interoperable implementations, by the looks of things.
As for the bridge, that is exactly what we'd like to do, as I've said before.
And customer support time and developer time devoted to this would cost money and represents an opportunity cost as well and that's a fact, not a point to be conceded.
And like I've said before, what you'd like to do and what you are doing are different. Nothing stops you from open sourcing it today. Put in comments that the APIs you use are not officially supported if you must. Open source it! It should have been open source a year ago! Open source it!
Some people are just like that :)
Great product, Proton team, thanks.
My understanding of Protonmail's argument (not that I agree with it) is they encrypt the full message, including headers upon accepting it. Based on my understanding of IMAP, you're effectively looking at a new protocol once you do everything needed to decrypt headers on the client-side.
Other than the Received, Delivered-To and Return-Path headers added by the intermediate MTA servers, every other header in the original message could be encryped, along with the message body when it's delivered to the server (or appended via IMAP).
Your suggested method basically is no different from any other provider. You rely on the sender encrypting the message and header information is entirely unencrypted on the disk.
I would prefer to see them promote standards to extend PGP rather than invest that time in a new, proprietary system with no buy-in from the email-related-software development community. I can follow the logic but I can also see their eyes lighting up when they realize this is a great excuse for having a proprietary, locked-in platform.
>It also encrypts the messages received that weren't encrypted when they weren't first sent
This could be done with PGP