In Outlook 2013 (and all earlier versions), it can't sort messages based simply on the sender's email address but rather prefers to sort them on the username that they use in their particular email client.  This is really frustrating and I can't believe it hasn't been corrected in Outlook 2013.

For example, I'm trying to scan through emails from one person, who always uses the same email address, yet Outlook sees her messages as from FOUR different people because she has entered her name differently on her various computers/mobile devices/email apps etc (e.g., full name, or first/last, or just first name etc).  So I have to browse FOUR different batches of messages to review them all, rather than seeing one sorted batch.

Please tell me how to sort based on email address alone!

If you use the search box in Outlook to search for the email address itself, you should find that it lists all messages from that person, regardless of what their display name is set as.

Alternatively, as long as Outlook as indexed the messages already, if you open one of the messages from the chosen contact into a new window you should see the People pane at the bottom with icons showing those people involved in that message. Clicking on the icon for the required person will expand that pane and show you all activity between you and that person, again regardless of how their name is displayed.