Previous versions of OWA didn't let you look at mail headers. In Exchange 2007, you can. Open a message in OWA by double-clicking on it or hitting Enter, then click on the "Message Details" icon.
The message details will come up in a nice dialog:
That should be quite popular!
Updated Jul 01, 2019
Version 2.0The_Exchange_Team
Microsoft
Joined April 19, 2019
Exchange Team Blog
You Had Me at EHLO.