Use P2? Use email? Use both!
We were using Jetpack to get notifications when new posts were published. Somehow Jetpack got disconnected from our site, and the connection could not get re-established. We've got an open ticket with the Jetpack team to fix, but I ran across this plugin and it does a better job than what we were using Jetpack for in the first place.
It took some testing to figure out that every user except the author of a post/comment receives the default email notifications (adjustable per user in their profile settings) but now my team can engage in the conversation right from the convenience of their email. This is exactly what we needed!! Many thanks to the developers!! :)