This article explains how to enable the full message source in Outlook email messages. It includes information on how to then view the full source of specific emails as they arrive. The instructions in this article apply to Outlook 2019, Outlook 2016, Outlook 2013, Outlook 2010, and Outlook for Microsoft 365.
Check Outlook Email Message Source
Outlook takes messages it receives from the Internet and stores the headers and individual message parts separately from the message body. When you select a message, Outlook gathers the parts to show only what is needed. Except when you want Outlook to show the headers. By default, Outlook removes certain header lines. Here's how to configure Outlook to retain the full source of email messages.
Open the Registry Editor. Go to the Windows Search box, type regedit and press Enter. Or right-click the Windows Start button, select Run, type regedit and select OK.
Navigate to the Windows Registry folder for your version of Microsoft Outlook:
