Finding problems with email headers in Outlook
It's easy to find the header for an email message in Outlook. Follow these steps. (I'm working with Outlook 2016 in this example).
1. With a message open go to File . . . Properties
2. In the Properties dialog box the message's header information will be listed at the bottom.
An email header may make reference to an IP address. A forged email may use an IP address that does not match up with domain listed in the sender's email address. If you get an email from firstname.lastname@example.org which the header indicates came from the IP address 220.127.116.11, you can confirm that the sender is from the edrm.net by checking its IP address with the tracert command in Windows. The IP address is the number listed at the end of the line beginning, 'Tracing route to . . .'
It's also a sign that an email has been forged if it's purports to be from a particular email client but its Mail User Agent format varies from the official pattern.
A list of common MUA header formats can be found here.