E.4 Message Body

The message body follows the message headers. The two components are separated by an empty line. Everything before the empty line is considered to be a header, and everything after the empty line is considered to be the message body.

Although the "format" of the message body is not necessarily specified in RFC 822, there are some standards that apply. Although any type of content can be sent over SMTP, messages that do not conform to these standards will not make it across the Internet's SMTP network. For example, messages that contain 32-bit binary objects will not likely make across a multiple- hop mail route, since some of those systems will only support 7-bit ASCII characters.

There are two popular encoding techniques in use today which will convert extended data into 7-bit ASCII. These techniques are UUENCODE and MIME. UUENCODE is based on free technology that has been around for a long time. However, UUENCODE has several limitations which prevent its use in many situations. In order to get around these problems, MIME was developed as a mechanism for providing rich content over an e-mail transport.

UUENCODE and MIME are not only limited to attachments. They can also be used to relay extended characters such as those found in Asian and European dialects. For example, the sample message shown in is in English and does not use any extended ASCII characters found in non-English languages. However, many nations use extended characters that are not found in the 7-bit ASCII character set, and these messages require encapsulation in order to be sent across the Internet reliably.

For more information on UUENCODE, refer to section E.4.1 UUENCODE and UUDECODE. For more information on MIME, refer to section E.4.2 Multipurpose Internet Mail Extensions (MIME). For more information about the envelope, refer to section E.2 The SMTP Envelope. For more information on the headers, refer to section E.3 Message Headers.

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