Overview

Threading messages on your iPhone can help users related emails similar to that on Gmail. The advantage is that it allows the user to easily trace back an e-mail conversation without having to search through the inbox.  If you want to turn off threading read this.

Tip 1 - Organize Messages by a Thread

Organize messages by a thread allows emails to show up as a single entry in the mailbox.  A number next to the right-pointing arrow in the entry indicates how many prior messages are in the thread.  In the below example, the number 6 next to Robert's message (left pane) indicates that six messages are part of this thread.  Once you tap that listing, the six threaded messages appear, as shown on the right pane.

Image courtesy of: dummies