MIME - Multipurpose Internet Mail Extension

Question 1

MIME - header fields

Answer 1

• MINE version - identifies the MIME version
• Content type - nature of the message
• Content transfer encoding - how the body is wrapped for transmission
• Content description - human-readable writing string telling what is in the message
• Content ID - unique identifier

Question 2

MIME - intro

Answer 2

• extension to RFC 822 for message format
• additional lines in message header declare MIME content type

Question 3

MIME - general characteristics

Answer 3

• extends and automates encoding mechanisms - Multipart Internet Mail Extensions
• allows inclusion of separate components - programs/pictures/audio clips - in a single mail message
• sending program identifies the components, so receiving program can automatically extract and inform mail recipient
• separator line gives info about specific encoding
• MIME is extensible (sender and receiver agree on encoding scheme) & compatible with existing mail systems
• everything is encoded as ASCII
• headers and separators ignored by non-MIME mail systems
• MIME encapsulates binary data in ASCII mail envelope

Question 4

MIME Transfer Encodings

Answer 4

• reliable delivery across large range of environments
• content transfer encoding field takes on 6 values: three of them (7bit, 8bit, binary): no encoding done (provide some info about nature of data; SMTP transfer uses 7bit form)
• quoted-printable - data contains largely printable ASCII characters; non-printing characters are represented by hex code
• Base64 (Radix-64 Encoding) - maps arbitrary binary input (6 bits) onto printable output 8 bit characters
• X-token - non-standard encoding