I use Gmail with the default Mail app. When you swipe left on the individual message in the Message List, your 2 choices are not grey More and red Trash?
I have my iPhone 5 and iPad 4 still running iOS 6. When I go to
Settings > Mail > Account there is a choice for toggling Archive Deleted Messages ON/OFF. On my iPad Mini-R, running iOS 7, following the same path, there is no option for that choice. I retain the function on the iPad Mini-R because it is selected for my Gmail accounts on the other 2 iOS 6 devices.
I can't find the Setting for Delete instead of Archive in iOS 7, either. There is an Ask Before Deleting toggle but that's about it.
Although I don't need it, I'd like to know the answer to this one, too.