Programming Internet Email

Mail with Attitude

The basic Internet mail system based on RFC 821, “The Simple Mail Transfer Protocol,” and RFC 822, “Format of ARPA Internet Text Messages,” succeeded in bringing order from chaos in the early Internet. However, the approach left much to be desired. Specifically, simple text Internet mail is generally criticized on two grounds: lack of security and inability to include arbitrary binary content.

Although developed to extend the Internet mail system, MIME has many uses. For instance, it is a key enabling technology for the World Wide Web, where it is used to differentiate file types downloaded to a Web browser. These additional uses of MIME are beyond the scope of this book.

MIME is sometimes called “Multipart” or “Multimedia” Internet Mail Extensions. Note that both of these names are incorrect. MIME allows multipart messages but is a multipurpose format. It was in use well before “multimedia” became a buzzword.

The greatest advantage that X.400 mail (or any of a number of proprietary mail systems loosely based on X.400, such as those from Microsoft, Hewlett-Packard, and Digital Equipment Corporation) had over simple Internet text mail was the ability to attach arbitrary types of files to a message. In this way, word processing files, spreadsheets, and audio or video files can be sent via email. MIME added this ability to Internet mail.

A MIME-compliant MUA can attach arbitrary binary content to an email message and send it to a MIME-compliant MTA for transfer. A receiving ...