I'm finding with this Discourse thing that I get a whole lot more private messages than I used to get with Google Groups. The ones from users seem to have died down after the tackily named "get a room" setting was increased (the number of emails before Discourse suggests having a private conversation).
My own preference is that we put everything related to Stan development on Discourse that doesn't contain private information. Even if you think it's just a quick note and not everyone is going to care. So rather than just sending me email, if you really feel you need to reach me, put the message on Discourse, then send me email with a link.
The problem may be due to my taking a page out of Andrew's book by drastically cuttting down on the number of times I check email or Discourse in a day. If you're emailing me or others because you don't think they'll get to Discourse soon enough, then please put the message on Discourse and email me a link. But as I said, I'm intentionally trying to be less responsive in the hopes I can actually do some programming and writing from time to time rather than spending all my time directing email messages. (One of the more depressing academic stories I ever heard was from the President of Carnegie Mellon, who told me he spent four hours/day every morning on email triage---not doing anything but routing email to the right person to do something and then checking up that it'd been done.)