My iPad's Mail inbox disappear after viewing sent emails

Ensure that you have updated your iPad to the current version of iPadOS. The tags appended to your post suggest that you have an iPad Pro with iPadOS 26 installed; at the time of writing, iPadOS 26.7.1 and 27.0.1 are current.

If the problem with your Mail App persists with the current version of iPadOS, try a forced-restart - as this will often clear an isolated or post-update software issue:

Force restart iPad (models with Face ID or with Touch ID in the top button)

If your iPad doesn’t have the Home button, do the following:

1. Press and quickly release the volume button nearest to the top button.
2. Press and quickly release the volume button farthest from the top button.
3. Press and hold the top button.
4. When the Apple logo appears, release the top button.

If the problem remains after performing the restart, it may be necessary to reset your iPad settings. While this reset will not cause any loss of data, as a precaution, it is always wise to ensure that you have a current iCloud or iTunes backup before performing the reset:

How to back up your iPhone, iPad, and iPod touch - Apple Support

When you are happy to proceed, you can perform the reset from iPad settings:

Settings > General > Transfer or Reset iPad > Reset > Reset All Settings

If the problem still doesn’t clear, the next step is to reset the iPad to factory settings:

Restore your iPhone, iPad, or iPod to factory settings - Apple Support

Otherwise, you would be best advised to seek advice directly from Apple Support. You can contact the Support Team using the Support link at top-right or bottom-left of this page. Alternatively you can initiate and manage your support cases from Apple devices using the excellent Apple Support App. If not already installed, the App can be downloaded from the App Store:

https://apps.apple.com/app/apple-support/id1130498044

You might also visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to assist with troubleshooting:

Genius Bar Reservation and Apple Support Options - Apple

Thanks for the reply. Forced restart previously tried. As I live within 3 miles of an Apple Store I will pop into see them. FYI this is a recent issue, started within the last 3 weeks.