MIME (Multipurpose Internet Mail Extensions)

MIME

•       MIME (Multipurpose Internet Mail Extensions) is an Internet standard for describes message content types.

•       MIME refers to an official Internet standard that specifies how messages must be formatted so that they can be exchanged between different email systems.

•       MIME permits the inclusion of virtually any type of file or document in an email message.

‖ Specifically, MIME messages can contain O text O images

O   audio

O   video

o   application-specific data.

spreadsheets

word processing documents

MIME Features

•       Support of character sets other than ASCII

•       Content type labeling System

•       Support of non-text content in e-mail messages

•       Support for compound documents

Non-ASCII Character set support

•       Message header

o        content-type field

put in the header by the client program creating the e-mail for use by the client program used to display the received message

charset= optional parameter

•        if absent ASCII is assumed

•        Content-Type: text/plain; charset="ISO-8859-1"

o        ISO-8859-1 extends the basic character set of ASCII to include many of the accented

characters used in languages such as Spanish, French, and German. O US-ASCII is the standard character set used in the US

Content Labeling

•        a set of registered MIME Types that map to specific file types

•        MIME Types consist of :

a primary type

a sub type separated by a / ( as text/html)

•        Common Mime Types:

Non-text Content

•       To be sent through the e-mail system non-textual content must be converted (encoded) to ASCII for transmission and unencode back to its original format for display upon receipt.

•       originally done via uuencode MIME uses base 64 encoding (RFC 2045)

binary to text encoding scheme

targets A-Z, a-z,0-9, +,/

scheme:

•       take three byte of data, put into a 24 bit buffer

•       extract 4 six bit values

•       use each value as an index into:

o       ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqr stuvwxyz0123456789+/

•       this yields 4 ASCII characters