"With the client code being open source, everybody can build the client themselves, run it locally and verify that the open source code is being used. If we published the server code open source, this would not be the case: No one would be able to verify that the open source server code is actually running on our server - so publishing it is a bit pointless."

So we continue in the reality where Tuta runs code on their sever and it is a mystery. It could be an amazing application. It could be a cellular automata that runs an email server.

I think I might start calling these organic tech. Because they take a word we know, "open source", and then use it like the food companies used "organic" stickers.

The E2EE behind Tuta Mail and Proton Mail are designed to be restricted to their ecosystem. While I understand the reasoning behind the decision, it means that their services were designed to be proprietary.

Proton Mail supports PGP encryption for external communications, but I believe Proton Mail Bridge blocks users from sending PGP encrypted emails.

The vendor lock-in is so bad that some Proton Official Emails (specifically Zendesk Support and Standard Notes) still don't use any form of E2EE (not even PGP).