Numerous times, I have a Mail icon that shows I have mail, and in reality I don't have any that aren't read, even deleting and setting up the account again doesn't change the issue... any thoughts ?
Cleveland, AGray34 is dead right...
Also, bear in mind, if you use Exchange, and use the swipe to delete option, emails actually go the All Mail folder, and NOT Trash.
To truly delete, using Exchange, you have to 'move' an item to the Trash.
Here we go again..... all deleted email on Gmail exchange goes to All Mail and not trash. Doesn't matter how you delete on the iPhone. Gmail exchange inherently puts/labels deletes as archive. You cannot change this.