How to view message headers
An email message has an envelope, much like a traditional paper letter, which includes the details of the recipient and the sender - it's called the message header. Most email programs only display the From, To, Cc, Date and Subject fields of this header message.
Included in an email message's header, but hidden by default, are details on the path taken by a message, from the point at which the message was sent, until it was delivered. These are very useful tracking details and diagnosing delivery problems.
Viewing message headers in Outlook: