Hi and welcome to the Forum. I'd say the app is causing the problem. Double click your home button, this will bring up your multi task bar along the bottom. It will show all the apps that you have opened at one time or another. Long press one of these apps until they start to jiggle and red minus signs will appear above them all. Press all the minus signs, this will close them, not delete them. It's a good idea to do this regularly just to keep them all running smoothly, I do mine every night. See if you can access the mail app now, if not a restart is in order. Press and hold the power off button, the one at the top right. You will see a slide appear to power off, slide this and the screen will go dark and a Whirly will appear. When the Whirly disappears your iPad is now off. Press the power button again until the Apple logo appears, this will take a few seconds and your iPad will start again. You should restart your iPad occasionally also as it will help the iPad to run smoother. Now see if your mail is operating. If not you will have to do a reset. Hold the power off button and the home button simultaneously, keep holding them in and you will see the power off slide appear and disappear, wait until you see the Apple logo appear before releasing the buttons. It will take a little longer for your iPad to start. This is a reset. When your iPad starts to play up, these are the first steps you should do to clear it. Let us know how you go, good luck!!