This past weekend, I stopped receiving email notifications. After looking into the problem, I noticed that my accounts were no longer set up to sync.
I searched around for a solution and found that several people in the past had this same problem with the following symptom; the check boxes to sync gmail, contacts, calendar, etc. no longer existed. The solution posted was to do a factory reset of the phone. That is the only solution that I could find.
I did the factory reset, and it solved the problem.
In re-customizing my phone, I noticed the REAL problem, which I share so that people don't have to do a reset.
1) Add Android Widget > Power Control
2) Turn on the second from right button (sync)
3) the check boxes will now appear under the Account for sync-ing
4) Then you can delete the widget from the screen if you want. (I like it, but others seem to hate it with a passion).
This is an embarrassingly easy solution. It is so simple that most people probably assume that you have already checked for this solution before complaining about the lack of sync.
Hopefully this saves someone out there from doing a factory reset.