Outlook 2016, 2013 & 2010 allow users to see header details of any email message using the option available as part of the Info menu.
Open the email message for which you want to see the header details.
Then click the File menu and navigate to Info menu option.
Click the Properties button under the Info menu. This would display the following Properties window.
The Internet headers section in the Properties window will have the full header details of that email message.