This article explains how to view the full email headers in Outlook.com. This information applies to Outlook.com and Outlook Online.

When you want to trace spam to its source and report it to your ISP, or when you want to see mailing list commands hidden in header lines, view the full headers for the message. By default, Outlook.com shows only a few important headers, but you can choose to show all header lines.

To access the full message headers in Outlook.com:

Open the message for which you want to view the headers.