Email folders missing from ipad

Assuming that you are using an IMAP or POP3 mailbox (this being most common with domestic email services), you need to verify that the seemingly absent email folders/messages are still present on your email providers servers. Log-in to your email providers webmail service, using a web browser, to verify that the email is still present in your account.

If the missing mail and folders is not accessible using webmail, the messages have been lost. If the missing content is visible, then you should be able to resolve the problem without too much difficulty.

After verifying that the email is still on the server, if you continue to have difficulties retrieving it using your iPad Mail App, you will need to delete the email account from your iPad - and then force-restart the iPad.

To delete the account:

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

Force restart your 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.

After performing the forced-restart, you can re-add the email account to your iPad:

Add an email account to your iPhone, iPad, or iPod touch - Apple Support