Why would you prefer XMPP? Last time I checked most features (like E2EE) weren’t part of the base protocol.
Just because it is not part of the base protocol, it doesn't mean it doesn't exist or supports it.
I like it for personal reasons. Just because is lightweight and there are way much more servers than matrix, imho makes it better. However, In the end it boils down to personal preferences and your attack surface.
It supports mail, but also has an encrypted normal chat backend AFAIK
WHen i tried it years ago, it was just a normal email with a special subject that the delta chat client would read, parse and display.
Email isn't a good protocol for instant messaging (it wasn't designed for real time communication and it lacks some features like typing indicators or voice/video calls)