Internet E-Mail Format

The format of mail used in Internet is defined by RFC-822, RFC-822. The format of headers is quite simple. The entire header is encoded in 7 bit ASCII as lines of text. Furthermore, RFC-822 only specifies a format for messages and does not specify any delivery mechanisms. The simplicity and flexibility of the format of RFC-822 messages are its main strengths, as it can easily be implemented on all systems. It is also its weakness: support of non-ASCII character set is missing; the structure of the header is very limited and body of messages are unstructured. The entire scope of Internet e-mail can be defined as RFC-822 compliant.

Extensions to RFC-822 exist that address its shortcomings. Many of these extensions are described in this paper.

In 1988, a Content-Type header field was added to Internet mail messages. RFC 1049, RFC-1049, recognized the need for using the mail system for sending around information with a greater degree of structure, while remaining within the constraints imposed by the limited character set.