https://wiki.xmpp.org/web/Jabber_Email_Header
Tell the world that you use XMPP by including a “Jabber-ID” header in your outgoing email. This page describes how to set that up in various email clients.
Ha, that’s soooo geeky! 
I use Fastmail, and rarely check email headers, so not really something I’m gonna do, but it sounds great for a shell account with local mail.