Email headers are pieces of code that allow mail servers and email programs like Windows Live Mail to route email on the internet, from the sender to the recipient; they also include "meta" information like to what address should the reply go, was a read receipt requested, was the message sent with high importance, etc. Windows Live Mail lets you view these headers with a couple of clicks, regardless of how a message was sent.
Right-click on the email in the folder listing and choose Properties (last at bottom). When the dialog opens, you'll get basic information about the message, including subject line, sender, date, and size. To view the full email headers, click on the "Details" tab at the top. Click inside the "Internet headers for this message" text box: 
Scroll up, down, and sideways, or right-click and choose "Select All", then "Copy" to save the headers and/or paste them into a text editor for easier reading.
Tip: when a message is selected in the folder listing, you can hit the Alt+Enter keyboard shortcut to open the Properties window; when an email is opened in its own window, select "Properties" under the message's menu (pictured right).
You get the headers in the scrollable text box: they represent all the "meta", hidden information that travels with your emails, used mostly by mail servers and relays around the world. To "View Source
", and see the underlying code behind the message body, click on the "Message Source" button (bottom right). A text editor will open, showing email headers at the top and the message's full HTML source at the bottom: 
By default, Windows Live Mail displays basic headers (from, to, date, etc.) both in the folder listing and at the top of the reading pane: columns on the left may vary. 
To hide these headers from the message preview, click on the View tab in the ribbon, and click on the "Reading pane" dropdown button: choose "Show message header in the reading pane
" at the bottom of the menu (do the same to resume showing them!) 