Re: E2E encryption
If they're doing it right the protocol should be XMPP perhaps with a simple IMAP extension to let the mail client know that XMPP is available and how to configure the chat client on the client side. Thunderbird has XMPP chat built-in already.
If they're really doing it right, you should be able to use your own XMPP server if you like and flick a switch on Dovecot to get the IMAP extension.
There are a lot of XMPP clients about and it'd be a shame to waste them.
Biting the hand that feeds IT
