Are you using the mail app that comes pre loaded on your device? One of my friends had trouble setting that up once but as far as sending emails I can't really think of much. You might want to try to reset your device by turning it off to try to clear something. When I bought my iPad one of the employes suggested that I turn of my iPad every so often otherwise things can run slowly. The last thing I can think of is dubble clicking the home button (or swiping with four fingers up) in certain cases and then tap and hold on the icon of the app that you want to actually close. When you exit out of the app by using the home button you are not actually fully closing the app doing so will. Try this with your mail, I hope it helps, if not try to go to the Apple store.