An email message internet header shows the raw message received by a email client. Calling this data a ‘header’ is a bit misleading because the data in the so-called header includes the entire email message plus a list of technical details about the message. The technical part of a email headers include tracking information for an individual email, detailing the path a message took as it went through various mail servers. The headers contain time-stamps, IP addresses and sender/recipient information.
Some senders use spoofing to disguise their email address. By checking the header, you can find out if the email address is different than it appears, and add it to your blocked senders list.
View message headers in Outlook on your desktop
Double-click an email message to open it outside of the Reading Pane.
Click File > Properties.
Header information appears in the Internet headers box.
Tip: You can highlight the information in that box, press Ctrl+C to copy, and paste it into Notepad or Word to see the entire header at once.