Mail app has stopped working on iPad 2

I haven't seen a thread quite on this topic: my email app suddenly died on my iPad 2. It was fine one minute and the next time I went to check the mail, it just loops back to the home screen. I've tried soft and hard reboots, shutting off the accounts (2 Gmail and 1 Exchange) and turning them back on again, but when I hit the mail button, it goes to a mail screen with no messages showing, waits about 20 seconds, then loops back to the home screen. Any suggestions?