I checked the message tracking logs on Exchange and nothing was ever leaving the OpsMgr server.  I tried to telnet to the smtp server and that worked.  I checked the logs and there was an innocuous message about the “Instant Notification” settings I were using, and how it was causing a notification workflow.  The app log message looked like this:

The exception text is:
Microsoft.EnterpriseManagement.HealthService.ModuleException: The specified Uri : (sip:email@im.vanity.com/home) has one or more invalid elements. A valid sip uri should be of the format sip:user@host.
Parameter name: uri —> System.ArgumentException: The specified Uri : (sip:email@im.vanity.com/home) has one or more invalid elements. A valid sip uri should be of the format sip:user@host.
 

(insert lenghty description of lots of things going crunch)

For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.

So I decided it was important to revisit my IM settings, since I knew that was what I was working on the day notifications had stopped. And there it was glaring at me in the face. the last thing I changed was added “/home” to the “Return Address” under the notification settings.

Once I removed that I proceeded to get 2 days worth of back-logged alerts. It is interesting to note that an error with the IM notification workflow actually affected the Email notification also.

I’m just happy I found it and fixed it. In case anyone ever sees the Event ID 4509 on your RMS, I would suggest visiting your notification settings.