MIME (Multipurpose Internet Mail Extensions). RFC1521. Originally an extension of SMTP (Internet e-mail) proposed in 1991 by Nathan Borenstein of Bellcore. MIME allows non-US-ASCII textual messages, non-textual messages, multipart message bodies, and non-US-ASCII information in message headers. In other words, MIME enables the attachment of multi-media and multipart encoding. MIME's utility has been to extended to more apps than just e-mail. EG: Browsers also use MIME to identify the content of documents.

MIME relates content with a content type, ie a combination of media type and subtype. There are seven standard top-level media-types:

• Discrete
  • application
  • audio
  • image
  • text
  • video
• Composite
  • message
  • multipart

The syntax of a content type is type/subtype (eg image/gif). The extension and media type help match data with the appropriate application in much the same way that a file extension does.

Here are some media types registered with the IANA (Internet Assigned Numbers Authority).

Type        Subtype                   Description                           Reference
----        -------                   -----------                           ---------
text        plain                     raw text                              RFC1521
            richtext                  simple SGML-based attributes          RFC1521
            enriched                  enhancement of richtext               RFC1563
            tab-separated-values      plain text w/ tabs
            html                      Hyper-Text Markup Language	   RFC1866
            sgml                      Standard Generalized Markup Language  RFC1874, SGML
            vnd.latex-z
            vnd.fmi.flexstor

multipart   mixed                     multiple content types                RFC1521
            alternative               alternative types for same content    RFC1521
            digest                    digest of message types               RFC1521
            parallel                  simultaneously viewes                 RFC1521
            appledouble               Apple-proprietary
            header-set
            form-data                 HTML form data                        RFC1867
            related                   inter-related parts                   RFC1872
            report                    status reports                        RFC1892
            voice-message             voice mail                  	   RFC1911
            signed                    digitally signed                      RFC1847
            encrypted                 encrypted                  	   RFC1847
            byteranges                data                                  RFC2068

message     rfc822                    ARPANET Mail                          RFC1521
            partial                   segmented Mail                        RFC1521
            external-body             external reference                    RFC1521
            news                      NNTP posting                          RFC1036
            http                      Hyper-Text Transfer Protocol          RFC2068

application octet-stream              generic binary                        RFC1521
            postscript                Adobe's Postscript                    RFC1521
            oda                       Office Document Architecture          RFC1521
            atomicmail
            andrew-inset
            slate
            wita                      Wang Info Transfer
            dec-dx                    Digital Doc Trans
            dca-rft                   IBM Doc Content Arch
            activemessage
            rtf                       Rich Text Format                      RTF
            applefile                 Apple proprietary
            mac-binhex40              BINHEX-encoded binary                 RFC1741
            news-message-id                                                 RFC1036
            news-transmission                                               RFC1036
            wordperfect5.1            WordPerfect
            pdf                       Adobe's PDF
            zip                       PK ZIP compressed archive
            macwriteii                Apple Writer II
            msword                    MS Word
            remote-printing           printer file                          RFC1486
            mathematica
            cybercash
            commonground
            iges                      International Graphic Exchange System
            riscos
            eshop
            x400-bp                   X400 body part                        RFC1494
            sgml                      Standard Generalized Markup Language  RFC1874, SGML
            cals-1840                                                       RFC1895
            pgp-encrypted                                                   RFC2015
            pgp-signature                                                   RFC2015
            pgp-keys                                                        RFC2015
            vnd.framemaker
            vnd.mif
            vnd.ms-excel              Microsoft Excel Database
            vnd.ms-powerpoint         Microsoft Powerpoint Presentation
            vnd.ms-project            Microsoft Project Schedule
            vnd.ms-works              Microsoft Works Wordprocessing
            vnd.ms-tnef               Microsoft Exchange Text Formatting
            vnd.svd
            vnd.music-niff
            vnd.ms-artgalry
            vnd.truedoc
            vnd.koan
            vnd.street-stream
            vnd.fdf
            set-payment-initiation
            set-payment
            set-registration-initiation
            set-registration
            vnd.seemail
            vnd.businessobjects
            vnd.meridian-slingshot
            vnd.xara
            sgml-open-catalog
            vnd.rapid
            vnd.enliven
            vnd.japannet-registration-wakeup
            vnd.japannet-verification-wakeup
            vnd.japannet-payment-wakeup
            vnd.japannet-directory-service
            vnd.intertrust.digibox
            vnd.intertrust.nncp

image       jpeg                      JPEG                                  RFC1521
            gif                       Graphics Interchange Format           RFC1521, GIF
            ief                       Image Exchange Format                 RFC1314
            g3fax                     Group3 fax                            RFC1494
            tiff                      Tag Image File Format
            cgm                       Computer Graphics Metafile
            naplps
            vnd.dwg
            vnd.svf
            vnd.dxf
            png                       Portable Network Graphics             PNG
            vnd.fpx
            vnd.net-fpx

audio       basic                     generic binary .au, .snd              RFC1521
            32kadpcm                  Internet Voice Mail                   RFC1911
            vnd.qcelp

video       mpeg                                                            RFC1521
            quicktime                 Apple proprietary
            vnd.vivo
            vnd.motorola.video
            vnd.motorola.videop

Here are some common experimental Content Types:

Type        Subtype                   Description                           Reference
----        -------                   -----------                           ---------
text        x-write                   MS Write

application x-cpio                    file transfer
            x-meme                    3D description language
            x-gzip                    GNU compressed archive
            x-compress                unix compress
            x-javascript              Java shell
            x-tcl                     TCL shell
            x-sh                      unix shell
            x-csh                     unix cshell
            x-gtar                    GNU archive
            x-tar                     unix archive
            x-shar                    archive
            x-zip-compressed          PKZIP compressed archive
            x-stuffit                 compress
            x-msdownload              file transfer/installer

image       x-MS-bmp                  MS bitmap .bmp
            x-rgb                     .rgb
            x-portable-pixmap         XWindows .ppm
            x-portable-graymap        XWindows .pgm
            x-portable-bitmap         XWindows .pbm
            x-portable-anymap         XWindows .pnm
            x-xwindowdump             XWindows .xwd
            x-xpixmap                 XWindows .xpm
            x-xbitmap                 XWindows .xbm
            x-cmu-raster              .ras

audio       x-pn-realaudio            Real Audio
            x-wav                     MS .wav
            x-aif                     .aif, .aiff, .aifc

video       x-msvideo                 MS .avi

x-world     x-vrml                    Virtually Reality Modeling Language    VRML

A newer version of MIME is S/MIME (Secure MIME) that supports encryption via RSA's public key encryption method. See my section on Encryption.