If you're having trouble with an email account, it may be easiest for you to remove and re-add the account.
TO REMOVE ACCOUNT
From the home screen, tap Settings.
tap “Mail Contacts, Calendars”
From the Accounts section, tap the email account you wish to remove.
tap “Delete Account”.
tap “Delete” to confirm.
TO ADD ACCOUNT
In Settings > “Mail Contacts, Calendars”…
In the Accounts section, Tap “Add Account”.
tap your email provider (AOL, for example), or use "Other" if not listed
Follow the onscreen steps and provide the required information to configure your account. In the boxes provided you should enter your name, complete email address, password, and a description of the account.
Once you’ve entered your information, in the top right, tap Next.
After your account has been verified, in the top right, tap Save. (Note: Make sure that the Mail option is turned ON.)
When the account setup has been completed, test that it works properly.
Thanks and good luck!