View RAW message source of an email in Outlook 2013

Headers

1. Open the particular email in a new window by double-clicking on the message in the message list. (This is important, it's not enough to be just looking at the message in what Outlook calls the 'reading pane'.)
2. Follow the menu File | Info | Properties
3. Look for a text area labelled Internet headers
4. Here are the headers. Select and copy the text to a text editor.

Content

1. Open message in a new window
2. On the Message ribbon, select Action | Other Actions | View Source.

1. Open message in new window
2. On the Message tab select Actions dropdown (next to Move button)
3. Select Other Actions → Source

Is File - Info - Properties not working to display the headers?

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This answer is from here: email.about.com

Make the complete message source available in Outlook

To set up Outlook so you can see the complete source of emails:

Press Windows-R
Type "regedit".
Hit Enter.
For Outlook 2013:
    Go to HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\Options\Mail
Select Edit | New | DWord from the menu.
Type "SaveAllMIMENotJustHeaders".
Hit Enter.
Double-click the newly created SaveAllMIMENotJustHeaders value.
Type "1".
Click OK.
Close the registry editor.
Restart Outlook if it has been running.

See the complete source of a message in Outlook

Now you can retrieve the source of newly retrieved POP messages (editing the SaveAllMIMENotJustHeaders value does not restore the complete message source for emails that were already in Outlook):

Click on the desired message with the right mouse button in the Outlook mailbox.
Select Options... from the menu.
Find the message source under the (now improperly named) Internet headers: section.