Folders in email have disappeared..how to retrieve

You may need to delete the email account from your iPad - then restart the iPad and re-add the email account. If using IMAP, your email and folders should safely remain on the mail server.

To remove the account from your iPad:

Settings > Mail > Accounts > [Your email account] > Delete Account

Restart iPad:

• On an iPad with a Home button: Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.
• On other iPad models: Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the top button. When the Apple logo appears, release the button.

Re-add email account to iPad:

Settings > Mail > Accounts > Add Account