The BODY, displays the e-mail message itself.

The HEADER appears at the top of the message. It usually contains: (1) the sender; (2) recipient(s); (3) the Subject Line; (4) the Carbon Copy line; and (5) possibly a Blind Carbon Copy line.

The information contained in the HEADER is readily accessible by the sender of the e-mail. A recipient will be able to view all components of the HEADER, except for the Blind CC e-mail address, which does not appear in the sent message. The Subject Line may reveal whether the parties have responded to a previous e-mail from the sender (RE:) or whether the sender has forwarded an e-mail from a third party to the recipient (FWD:).
For a user-friendly guide to understanding and using e-mail, please see: www.learnthenet.com.