How to Delete All Mail
By Conner Carey
Finally, in iOS 9, there is an option to delete all of your mail via the Mail app. This only works with individual mailboxes, such as Yahoo, not the All Inboxes mailbox. If you're using Gmail, you'll need to select Delete All instead of Archive All in Gmail Settings. If you're worried about losing emails you want to keep, there's a setting you can enable to prevent accidentally deleting emails.