Sometimes when you add an existing Email account to iPad, your iPad downloads emails from your mail server to the iOS device and all emails are marked as unread. However you know you have already read them on another device. How can you mark all emails as read on iPad?
If you have setup your email account iPhone, you can refer to this page: how to mark all emails as read on iPhone?
Mark All Emails as Read on iPad
Open the Mail app for iOS on your iPad, select the email account you like to manage and edit its emails.
Tap on the Edit icon on th top, you will be able to select emails to edit on iPad. You can tap on the emails one by one to select multiple emails to modify. To select all messages, tap on the Mark All button on the bottom left corner, see below screenshot.
When you tap on Mark All button, a dialogue shows up like below. There will be two options for your choice, Flag and Mark as Read. Now choose the second option to mark all emails as read on iPad. See below screen capture.