From a Home screen, tap Apps (located at the bottom).
If unavailable, tap the dropdown menu (located in the upper left) then tap Alphabetical. If still unavailable, refer to Manage App Icons.
Tap and hold the email message.
Message(s) are marked for deletion when a check mark is present.
To delete all messages, tap the Menu icon (located in the upper-right) then tap Select all. At least 1 message must be selected (checked) to mark all messages for deletion.