Outlook 2007/2010/2013
You can display full headers by double clicking on a message so that it opens in a separate window (not the preview pane).
Start Outlook.
Double-click the message for which you want to view full internet headers.
Click Options (2007) or Tags (2010/2013).
message options button /
The Message Options dialog box is displayed. The internet headers are shown in the Internet headers field at the bottom of the dialog box.