Unfortunately, Mail has stopped
A bug may have corrupted the app's data. You could try resetting the 'data' portion instead of just the 'cache'. This would essentially make the app reset to factory default (but only that app, not the rest of the phone).

You would have to redo all of your settings, but the important parts (emails) are on the exchange server, so it wouldn't be too difficult to get back to the way things were.