GM.
I guess the benefit of email is that it has become an agnostic protocol that can interact with almost any client?
Ideally you want to send a mail that opens as a gateway into a secure chat on any mail client and then removes the whole chat (cleaning up unnecessary and sensitive data), while leaving behind the key notes you wanted to chat about 😁
Combine security (temporary chat channel) through usability (remove need to install yet another client).
Not that this is feasible, but I didn't read that requirement 🤭