My mail app won't open on an iPad 2

Close the Mail app in the Task Bar and re-launch.

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.

If it still doesn't work, try a reset.

Hold the Sleep and Home button down (together) for about 10 seconds until you see the Apple logo.

iOS: Unable to send or receive email

http://support.apple.com/kb/TS3899

Can’t Send Emails on iPad – Troubleshooting Steps

http://ipadhelp.com/ipad-help/ipad-cant-send-emails-troubleshooting-steps/

iPad Mail

http://www.apple.com/support/ipad/mail/

Try a Reset - iPad How-Tos http://ipod.about.com/lr/ipad_how-tos/903396/1/

Or this - Delete the account in Mail and then set it up again.

 Cheers, Tom 😉