Internet Messages and SMTP

"Standard for the Format of ARPA Internet Text Messages" is the title of RFC 822, the document that has defined the format of Internet mail messages since its publication in August of 1982. This straightforward format has been very successful. In fact, it has been adopted, wholly or partially, well beyond the confines of the Internet and the Internet SMTP transport, which is defined in RFC 821.

A basic understanding of RFC 822 messages and MIME extensions is useful for people who use CDO to create MIME formatted messages. Many properties and methods, for example, IBodyPart.ContentMediaType, require that you have some understanding of RFC 822 and MIME.

As the RFC 822 message format has seen wider use, a number of its limitations have proven increasingly restrictive. These limitations and the ways they were circumvented are described more fully in MIME Extensions to Internet Mail.