Organizing your e-mail in Outlook 2010
Outlook 2010 has a great new feature for organizing messages by date and arranging them by Conversation. Using this feature, messages that share the same subject appear as Conversations that can be viewed and expanded or collapsed by clicking the icon to the left of the Subject line. The messages within each Conversation are sorted with the newest message on top. When a new message is received, the entire Conversation moves to the top of your message list, helping to make tracking email threads a snap.
To turn on Conversations, on the View tab, in the Conversations group, select the Show as Conversations check box. You can reduce the size of a conversation with the Clean Up feature, which deletes duplicate messages in the Conversation. On the Home tab, in the Delete group, click Clean Up, and then click Clean Up Conversation.
You can also sort your e-mails by Conversation in Outlook 2007 by right-clicking the Arranged by bar in the summary message panel.