email

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This lesson covers protocols for MIME.

MIME

  • Multi-Purpose Internet Mail Extensions
  • Internet standard that extends the format of email messages to support text in character sets other than ASCII, as well as attachments of audio, video, images, and application programs.
  • Message bodies may consist of multiple parts, and header information may be specified in non-ASCII character sets.
  • Email messages with MIME formatting are typically transmitted with standard protocols, such as
    • Simple Mail Transfer Protocol (SMTP)
    • Post Office Protocol (POP), and
    • Internet Message Access Protocol (IMAP).
  • In the HyperText Transfer Protocol (HTTP) for the World Wide Web, servers insert a MIME header field at the beginning of any Web transmission.
  • Clients use the content type or media type header to select an appropriate viewer application for the type of data indicated.
  • MIME header fields
    • MIME-Version: 1.0
    • Content-Type: text/plain
      • text/html, image/jpeg, audio/mp3, video/mp4, and application/msword
      • https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_types/Common_types
    • Content-Disposition: attachment; filename=genome.jpeg; modification-date=”Wed, 12 Feb 1997 16:29:51 -0500”;
      • an inline content disposition
        • automatically displayed when the message is displayed, or
      • an attachment content disposition
        • not displayed automatically and requires some form of action from the user to open it
      • Some mail user agents did not follow this fully
    • Content-Transfer-Encoding
      • set of methods for representing binary data in formats other than ASCII text format
      • It indicates whether or not a binary-to-text encoding scheme has been used on top of the original encoding as specified within the Content-Type header:
        • If such a binary-to-text encoding method has been used, it states which one.
        • If not, it provides a descriptive label for the format of content, with respect to the presence of 8-bit or binary content.