Delete All Emails in a Folder in iOS Mail
To delete all the messages from a folder in iOS 12, iOS 11, or iOS 10: The only folder that doesn’t require you to tap each email to select it is the Trash folder. After you tap Edit at the top of the screen, you can choose Delete All at the bottom to empty the trash folder without selecting individual emails.
Delete All Emails in a Folder in iOS 9 Mail App
Deleting messages is even faster in iOS 9 because you don’t have to tap each one. To delete all the messages present in an iOS 9 Mail folder: The Mail app in iOS 9 deletes all the messages in the folder, not just those you fetched to the device. If more messages are on the server, they are deleted as well. Deleting all messages does not work in iOS Mail smart folders such as Unread, VIP or Today. In addition to deleting email, you can move all messages in a folder and act on them in other ways.
