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.
Whether you see the Archive or Trash button depends on your email service. Gmail's inbox uses Archive, which moves emails out of your inbox without permanently erasing them. Most other services, such as Yahoo, have a Trash button instead.
To permanently erase messages from Gmail, perform this task in the All Mail folder instead of the inbox. While in All Mail, you'll see a Trash button instead of the Archive button.
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.
If you can access your email service through a website, you might find the Web interface easier to use for deleting multiple email messages than the Mail app. Gmail, Yahoo Mail and Outlook.com (Hotmail) all display mobile-friendly interfaces when you load them in Safari.