There is a lot you can do with the sorting feature in Outlook. You probably already know that you can sort your Inbox or another message folder in a multitude of ways by clicking on the appropriate header, such as Received or From. This can be so helpful when you are looking for a message from a particular sender, or if you want to keep your inbox in order by the dates you received the emails. You can sort your contacts, tasks and other Outlook items as well.

Sometimes, though, one header is not enough. In that case, you can sort your items twice. Click the first heading by which you want to sort, then press and hold the Shift key and click on the second heading.

For example, if you know you are looking for an email message from a specific coworker, begin by clicking the From heading. Once the senders are nice and alphabetical, you can press and hold the Shift key and select the Subject, Received or other heading. The email messages will still be sorted by sender, but they will also be “sub-sorted” by the second heading you selected.

You can do this for up to four columns, should you need to.

In addition, if you like some more structure when you sort, you can ask Outlook to arrange items in groups.

In Outlook 2003 or 2007, go to the View menu, point to Arrange By and select Show in Groups.

In Outlook 2010, go to the View tab and click on View Settings. Click the Group By button and select the Automatically Group According to Arrangement button.

Taken from http://www.officeusers.org/nlarchive.aspx