I had a problem where it seemed like email was not being pushed to my phone (Exchange). It was so frustrating that I was thinking of returning the phone.
I spent HOURS playing with all the settings, rebooting, etc. but no luck.
I decided to install the "Touchdown" email app in a last ditch effort to replace the built in email system.
Two things happened: (1) I got my Exchange email immediately in both the native and Touchdown email client and (2) I got two notifications, one from native and one from Touchdown.
So I played around with the settings... lost both notifications... and I think I figured the combination out that gives you just the native notification.
If anyone else has had experience with failed Exchange notifications and figured out a way to fix it other than installing a second email client, please let me know.
EDIT: It doesn't work anymore.