When browsing through and managing your e-mail, you will likely regularly use three tasks: flagging messages, deleting unwanted ones, and then marking any that you would like to revisit later as unread. This last option is especially useful if you access your e-mail on multiple devices. In the Mail app in iOS, you can do these tasks using the toolbar at the bottom of an opened e-mail message, but there are a couple of additional approaches that can be far more convenient.
These are done on the main message list, where you can swipe a message briefly to the left or right to reveal management options. When doing so to the right, you will see a blue square that allows you to mark the message as unread, and to the left will show options for deleting, flagging, and “more” for less common tasks like moving the message, or directly replying or forwarding without viewing its contents.
While sliding your finger and briefly swiping to then tap one of the revealed options might seem a trivial difference, when managing many e-mails in the small and relatively simple list in iOS, the slight speed advantage that these offer may make your task go a bit quicker.