This document explains how to sort messages using Apple Mail. These instructions are for Mac OS 10.9, but are likely to be similar for Mac OS 10.5-8.
To sort messages:
- Select the mailbox you'd like to sort messages in.
- At the top of the message list, select Sort by... or select View -> Sort By.
- A menu will appear with options to sort your messages.
- Choose whether you want to sort the messages by Attachments, Date, Flags, From, Size, Subject, To, Unread, Oldest Message on Top, and Newest Message on Top.