Fantastic. Thank you. I will make sure to read through the paper when I have some spare time.
This makes sense to me. And exactly as you say, this could happen with any e-mail provider. Does the same apply to e-mail desktop clients, too? If I am not mistaken, if your e-mail client is a FOSS desktop client (and not receiving JS from the server), you yourself can verify what is being sent between the server and the desktop client. If it is just encrypted messages only you can decrypt on your device, it could potentially mitigate this issue, no?