Multipurpose Internet Mail Extension MIME

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Multi-purpose Internet Mail Extension (MIME)

• By
• Neetu Bharti
• Trainee,NCSI,
• IISC,Bangalore-12
• 2001-2002
• Date of Presentation07/Mar/2002

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Contents

• Definition of MIME
• Introduction
• What exactly is MIME?
• How it Works?
• MIME-Specific Technical Definitions
• Example of MIME
• Summary

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Definition of MIME

• MIME, stand for Multi-purpose Internet mail
  Extensions, is a freely available specification
  that offers a way to interchange text in
  languages with different character sets, and
  multimedia e-mail among many different computer
  system that use Internet mail standards.

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Introduction

• MIME extends the format of Internet mail to allow
  non-US-ASCII textual messages, non-textual
  messages, multipart message bodies, and
  non-US-ASCII information in message headers.
• MIME provides Internet mail users with
  functionality similar to that of MS-Mail for
  LAN-based internal mail. MS-Mail and MIME allow
  the attachment of files and other objects, as
  does MIME. Unfortunately, Microsofts method of
  handling these attachments is undertaken through
  a proprietary format and MS-Mail does not provide
  compliance with the MIME open standard.

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Cont

• Internet messages with MIME attachments send to
  MS-Mail will transfer the appropriate text
  portions of the message, but MS-Mail will
  generally forward the attachments as encoded
  text, which may then be saved to a file and
  decoded. Conversely, messages sent from MS-Mail
  with attachments to an Internet MIME mail system
  will transfer the text portions and send the
  attachments as encoding text, but use a different
  method of encoding from the used by MIME and
  without the information needed for processing the
  message attachment by the recipient. Email
  messages arriving at the National Library with
  MIME attachments are likely to be corrupted.

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What exactly is MIME?

• In 1992, a new standard was defined by an
  Internet engineering task force working group in
  RFC1521 1522 called MIME.
• MIME is an extension to the Internet mail
  standard, known as Simple Mail Transfer Protocol
  (SMTP) that allows mail messages containing
  different type of multimedia information to be
  sent across the network this includes, but is not
  limited to, word-processor documents,
  spreadsheets, programs, graphics, audio, and
  motion picture files, as well as links that
  enable users to retrieve information from remote
  databases from within a mail message.

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Cont

• MIME is a specification for enhancing the
  capabilities of standard Internet e-mail.
• It offers a simple standardized way to represent
  and encode a wide variety of media types of
  transmission via Internet mail.
• It is defines extensions to SMTP to support
  binary attachments of arbitrary format.
• The designers of MIME have learned a lot from the
  old SMTP protocol and its mailers.
• MIME is here to stay and it works.

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Cont

• When using the MIME standard, messages can
  contain the following types
• Text message in US-ASCII
• Character set other than US-ASCII
• Multiple objects in a single messages
• Multimedia Image, Audio, and Video messages
• Multi-front messages
• Messages of unlimited length
• Binary files

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Cont

• MIME is defined to be completely backwards
  compatible, yet flexible and open to extensions.
  Therefore, it builds on the older standard by
  defining additional fields for the mail message
  header, that describes new content types, and a
  distinct organization of the message body.

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How MIME works?

• The developers of MIME found a clever way to work
  around the limitation. It packages different data
  types into a 7-bit ASCII format. that way, all
  e-mail, regardless of the data it contains,
  appears as standard e-mail messages to the
  internets SMTP servers. The beauty of the
  solution lies in the fact that SMTP didnt have
  to change to handle such data.

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Cont

• Uses a new binary encoding scheme called BASE 64
• New SMTP headers describe the attached document
• User agents read the header to figure out how to
  interpret the message

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MIME Specific technical definition

• New MIME headers
• The Content-type headers
• The Application-type headers
• The Content-transfer-Encoding
• The Content-ID Content Description
• Multipart Message
• Non-ASCII text in mail messages

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New MIME headers

• Required fields
• MIME - Version
• Date - Time

• Optional fields
• Content- type
• Content-transfer_encoding
• Content-ID
• Content-description
• Content-disposition

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The Content-type Header

• Content-type sub-type describes what format this
  part of the message is in
• Text Image
• Message Audio
• Application Video
• Multipart
• The default type is simple ASCII text
• MIME-Version 1.0
• Content-typetext/plaincharsetUS-ascii

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The Content-type Applications

• Subtypes
• Postscript
• Octet-Stream-Unidentified binary data
• Many other will be added

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The Content-transfer-Encoding

• Base64 encoding algorithm is used to encode
  binary data in 7bit ASCII data
• Quoted-printable is for text-only messages
• A few others
• 7bit No encoding
  Case insensitive
• 8bit No encoding
• Binary No encoding
• X-token No encoding
• Example

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Summary

• MIME has been designed to avoid problems caused
  by additional restrictions imposed by some
  Internet mail transport mechanisms.
• The Multipart and Message content types allow
  mixing and hierarchical structuring of objects of
  different types in a single message. Further
  content types provide a mechanism for tagging
  messages or body parts as audio, image, or other
  kinds of data.
• Finally, a number of useful content types are
  defined for general use by consenting user
  agents, notably Text/Richtext, Message/Partial,
  and Message/External-Body.

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Thank You.