Removing a single email in the iOS 8 Mail app only takes a leftward swipe and a tap of the Trash (or Archive button), but clearing out emails in bulk isn't quite as straightforward. To delete a selection of several emails at once, press Edit and select them one by one. If you want to wipe clean an entire folder, there's a hidden trick to save you from having to check each message separately.
Delete Multiple Emails
Tap Edit in the Mail app to display check boxes by each email. Check the messages you want to delete and tap Archive or Trash.
Empty an Entire Folder
Tap Edit in the Mail app and check the box by any single message in the inbox or other folder that you want to empty. Press and hold the Move button. Do not release the button yet.
While still holding down Move, uncheck the checked message using another finger. After unchecking the email, release the Move button.
Pick a location to move the entire contents of the folder. To delete the messages, choose Trash. If you use Gmail and want to archive the messages, choose All Mail.