This information applies to Outlook.com and Outlook Online.
By default,Outlook.comshows only a few important headers, but you could make it displayall header lines.
SelectMore actions(the 3 dots…in the upper right).
The header information will be at the top of the email.
You’ll see not only the header information but HTML formatting for the email as well.
SelectClosewhen you finish viewing the header information.
What Do Email Header Lines Look Like?
An email’s header lines can look like the following highlighted example below:
