HOWTO | Customise Gestures in iOS Mail
1 Left and right swipes
You can swipe left to right across a message to mark it as read or unread. Swiping from right to left works slightly differently. A long swipe to the left immediately deletes the email, but by swiping a little more slowly you’ll see additional options, such as the ability to flag the email for reading later.
2 Swipe away
You can change the way the gestures work in the Settings app > Mail, Contacts, Calendars > Swipe Options. The diagrams here show the currently assigned actions. Only the actions in the positions shown in blue are changeable. They are set to ‘Flag’ and ‘Mark as Read’ by default.
3 Customising gestures
Your options are fairly limited. If you tap on Swipe Right, you can change it to either flag the email or file it in the Archive mailbox. If you’re left-handed you might want to change the Swipe Left gesture to ‘Mark as Read’ so that the default actions are now reversed. But we’re not finished yet.
4 Mail Behaviours
In Settings > Mail, Contacts, Calendars, tap your iCloud account at the top, then Mail under the Advanced heading. Scroll down and tap Advanced to control which mailboxes are used. You could specify that discarding an email (a left swipe) puts it in the Archive mailbox rather than Deleted.