This is Nathan. Welcome to justanswer.
Close the Mail app in the Task Bar and re-launch.
Begin by pressing the hold and home buttons at the same time. The hold button is the one on the top right corner of the iPad. The home button is the round one at the bottom center of the iPad's front.
Double-click the Home button to reveal Task Bar. Hold Mail app down for a second or two; tap the minus sign to close app.
Does this solve your problem?
Try holding the Sleep and Home button down (together) for about 10 seconds until you see the Apple logo. Ignore the red slider.
This will surely solve your problem.
When you were doing the above step that i told you before, the mail app should be opened on the background
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