My email was not working correctly and was mixing messages between accounts. I tried to delete my main account and reinstall. It got locked in the delete mode and when I finally got it to stop I could not reinstall the account because the account name was still there. I was almost at the point of a hard reset to factory when I tried deleting all data and cache in the mail app. It cleared out all the email accounts and I reloaded them. Everything works great and BEST part is email is now much faster AND I picked up about 100 extra mb of internal memory! Phone must store emails in memory even though they are deleted.
Try this next time you have email problems you can't fix and before you do a factory reset.
Try this next time you have email problems you can't fix and before you do a factory reset.