[jayjader]

> if you log in on a new device and see all your content while using only login and password to authenticate yourself

What about if the encryption key is derived from your password? This is common enough for "encrypt file with a password" services, I've personally implemented it in-browser as part of a small project.

Now, having your account password be the same as the email decryption password is also probably a bad idea, but we're far from the server owner being able to read your emails.