Sort by time and date of receipt, placing the most recently received messages at the bottom.
Sort alphabetically by name of sender. This is useful for grouping together all the messages from a particular person.
Sort alphabetically by subject of mail, to group together all the messages about a particular subject.
Sort by the size of mail messages, from smallest to largest.
Sort by the "read" status of the mail. This puts the messages you have read first, the unread messages next, and the new messages last. This is useful to group together all your unread mail after you have read your messages in a non sequential order.
Sort by the message numbers.