As a consultant, I often find myself looking through Internet Headers to diagnose why a message made it through a spam filter. In Outlook 2003/2007, you could right-click a message and click Message Options to view the Internet Headers. Apparently Microsoft didn’t feel this was used enough, so it is now tucked away where nobody will find it in Outlook 2010. Now you need to open the actual message, then click File, Info, Properties.
You can also add this to the Quick Access Toolbar by clicking the little arrow in the upper right corner of Outlook and choose More Commands.
Change the Choose commands from: drop down list to All commands, and add Message Options to the Quick Access Toolbar. Click OK, and from now on you will have an extra button next to that little arrow.