The correspondence page allows you to review your entire correspondence with a particular person, ordered chronologically. You can also have this thread emailed to you, or move the entire correspondence with a person into the trash.

In order to help you keep track of messages, your correspondents are highlighted when it is "your turn" to write back, i.e. the most recent message in your correspondence with them was sent by them, not from you. The icon used is a tennis ball: ''.

Note, the correspondence page only displays (and counts) messages in your inbox and sentbox, but not your trash. However, it does check your trash when calculating whether it's "your turn" to write back. (Once you have permanently deleted a message, the correspondence page no longer knows about it).