View Full Email Headers in Outlook 2010/2013
Open the specific email message of interest in a new window by double-clicking its line in the email summary pane.
Go to the “File” tab in the new window and click on the “Properties” button.
Note: that if you go to the “File” tab in your main Outlook window (as opposed to the window that you popped up with a single email message), it will not have a “Properties” button, because these are specific to a single message rather than the whole application.
When you click the “Properties” button, a new Properties window should pop up:
The headers are in the bottom portion of the window. Copy and paste to an editor in order to view them in a more convenient manner.