Hey Outlook 2010, where are my message headers?

Now you tell me!  I had to figure this out a couple of days ago though I have trouble remembering that I already have it on the Quick Access Toolbar since the icon is not all that distinct.  However, discovering that which Quick Access icon does it is considerably easier than rediscovering where the option is buried.

Thanks for the clean, welcome explanation.  I find I need to see these a lot, especially for digging deeper into what may be fake postmaster notices and other suspicious e-mails.  I use the white-list approach to Junk E-mail, but I still need this to decide when to white-list something new or to deal with mail that appears to be from a known sender yet appears suspect.