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/
Setting up and troubleshooting Mail
http://www.apple.com/support/ipad/assistant/mail/
Server does not allow relaying email error, fix
http://appletoolbox.com/2012/01/server-does-not-allow-relaying-email-error-fix/
Why Does My iPad Say "Cannot Connect to Server"?
http://www.ehow.co.uk/info_8693415_ipad-say-cannot-connect-server.html
iOS: 'Mailbox Locked', account is in use on another device, or prompt to re-enter POP3 password
http://support.apple.com/kb/ts2621
iPad Mail
http://www.apple.com/support/ipad/mail/
Configuration problems with IMAP e-mail on iOS with a non-standard SSL port.
http://colinrobbins.me/2013/02/09/configuration-problems-with-imap-e-mail-on-ios -with-a-non-standard-ssl-port/
Try this first - Reset the iPad by holding down on the Sleep and Home buttons at the same time for about 10-15 seconds until the Apple Logo appears - ignore the red slider - let go of the buttons. (This is equivalent to rebooting your computer.)
Or this - Delete the account in Mail and then set it up again. Settings->Mail, Contacts, Calendars -> Accounts Tap on the Account, then on the red button that says Remove Account.
Cheers, Tom 😉