• 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 application-specific data.
word processing documents
• 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
• 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:
• 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, +,/
• 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