Be it for identifying the origin of spam, be it for fun, having a look at the raw source of an email message can be interesting.
View the Source of a Message in Mac OS X Mail
To display a message's source in Mac OS X Mail:
- Select View | Message | Raw Source from the menu.
- Alternatively, use the keyboard shortcut Option-Command-U (think source).
- In Mail 1.x, the menu item is Message | Show | Raw Source.
The same shorcut also takes you back to the original message, or you choose View | Message | Original Content (Message | Show | Original Content) from the menu.
(Updated July 2011)