The number of messages in the mailbox, the space those messages use, and the space wasted (see “Compact Mailboxes” in the “Special” menu)

This column displays the subjects of the messages.

This column displays the sizes of the messages, in “K” (1K = 1024 characters).

This column displays the date the messages were sent.

This column displays the people who sent the messages (or the recipients of the messages, if they're messages you created).

Drag this line to change the size of the Size column.

Drag this line to change the size of the Date column.

Drag this line to change the size of the Sender/Recipient column.

Drag this line to change the size of the Status/Priority column.