Correspondents Map
The correspondent map groups the messages in a collection by sender. Senders are further grouped by their domain. Within a domain, people are ordered by the number of messages they have sent, and people who sent more messages are shown first. If there are many senders, the rectangles are reduced in size to only show first names or initials. The color of the rectangles indicates the age of the most recent message from that sender.

The "unanswered" check box grays out the rectangles of the people to whom the user has sent mail more recently than he/she has recieved it (i.e., leaves the highlights on the people who are owed a response).