Notifications by xmpp

Instead of privacy leaky email consider an option for sending xmpp notifications with omemo.

I suspect that until an important enterprise customer wants such a feature you’re going to need a plugin. Depending on how you do it I think it would take a couple days or a couple of weeks (though I’m not familiar with the notification code, so it’s a wild guess). If you have a budget you could ask in #marketplace, if you’re a developer you could ask in #dev.