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The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)       9  TCP/IP Key Applications and Application Protocols            9  TCP/IP File and Message Transfer Applications and Protocols (FTP, TFTP, Electronic Mail, USENET, HTTP/WWW, Gopher)                 9  TCP/IP Electronic Mail System: Concepts and Protocols (RFC 822, MIME, SMTP, POP3, IMAP)                      9  TCP/IP Electronic Mail Message Formats and Message Processing: RFC 822 and MIME                           9  TCP/IP Enhanced Electronic Mail Message Format: Multipurpose Internet Mail Extensions (MIME)

MIME Content-Transfer-Encoding Header and Encoding Methods 1 2 TCP/IP Electronic Mail Delivery Protocol: The Simple Mail Transfer Protocol (SMTP)

All of the MIME mechanisms discussed in this section up to this point deal with ways of encoding different kinds of ASCII and non-ASCII data into the body of an RFC 822 message. In addition to these capabilities, MIME also includes a way in which non-ASCII data can be encoded into headers of an RFC 822 message.

At this point you might be wondering why anyone would want to do this. Sure, it makes sense to be able to use MIME to encode binary data such as an image into an e-mail, but why do it in a header? Well, if you can't see the need for this, chances are that you are a native English speaker. J ASCII does a great job of representing English, but isn't so hot with many other languages. With RFC 822, the speakers of languages that use non-ASCII characters were unable to fully use descriptive headers such as the Subject and Comments headers. Some could not even properly express their own names!

The solution to this problem is the subject of RFC 2047, the third of the five main MIME standards. It describes how to encode non-ASCII text into ASCII RFC 822 message headers. The idea is straight-forward: just as with message bodies, the non-ASCII text is replaced with ASCII, and information is provided to describe how this was done.

MIME Content-Transfer-Encoding Header and Encoding Methods 1 2 TCP/IP Electronic Mail Delivery Protocol: The Simple Mail Transfer Protocol (SMTP)