RFC 822 messages have two major parts:

  • Message envelope.  The message envelope contains all the information needed to accomplish transmission and delivery of the message. This information includes the e-mail address of the message's creator — also known as the originator. This string matches the information in the Sender: header, if this header is present. The envelope is created by a user agent (such as MS Outlook) and is meaningful only to the message transfer agents (MTAs) that move the message on the path to its destination.

  • Message contents.  The contents make up the object to be delivered to the recipient. Message contents consist of lines of ASCII text. This text is arranged in the classic "memo" format, in which the message contains one or more introductory headers and a body.

This structure can be seen in the following illustration:

Figure 19.2. The structure of an Internet mail

The structure of an Internet mail

Example 19.7. Simple Internet Mail Message

As you can see in the following sample of a message's contents, the format described in RFC 822 produces messages readable with little difficulty by humans.

The first few lines, from the first instance of "Received" to "Precedence", are headers. These lines define the recipients, the sender, the date, and other information involved with message transmission.

Following the headers is a blank line. This is marked by the consecutive occurrence of the four characters: CR, LF, CR, LF. After this blank line starts the body of the message. In the following example, only the final few lines make up the message body.

Received: from techsupp@openlinksw.co.uk
Message-Id: <v1214040cad6a13935723@>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Date: Mon, 4 Jun 1998 09:43:14 -0800
To: customer.services@openlinksw.co.uk
From: OpenLink Technical Support <techsupp@openlinksw.co.uk>
Subject: Happy Reading
Precedence: bulk

Hope you are enjoying this chapter,
Technical Support