> They don’t have a master key or else the whole e2ee story is a fad, which it isn’t

You can store an encrypted master key (like Luks), download that key to the client and decrypt it there. Or you can have it in decrypted in server memory, but only during an interactive session with the user. But that quickly turns into a fad, as you pointed out, which was exactly my question.

> The Proton code is in Github so you can check how it works yourself. Please think and do some work before you reply.

I asked a simple question, so that at others could chime in about the exact details and limits. I don't understand why that was highly offensive to you, but I assume it is something like a Monday Mood.