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
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