MIME (Multipurpose Internet Mail Extensions) is a format for passing a variety of information via internet mail. MIME defines a general data format within which a wide variety of data can be transferred. MIME prescribes a header, a category (type) that identifies the general type of information, and a subtype that is used to invoke a specific handler. For example, a Windows executable file would be identified as type-"application", subtype "octet-stream". The Octet-Stream handler will probably give the user the option of saving the data as a file, or of executing it. But it doesn't have to. MIME just gets the data to the right place. It doesn't care what happens to it.

The most frequently used types are:

There are more subtypes than can easily be listed. One source lists over 100 application subtypes for example. Since a subtype can be defined by any application, new subtypes are being defined all the time. "x-"subtypes are "experimental" thus guaranteeing that an x- name can not conflict with an accepted subtype.

MIME is defined in a series of RFCs. The most important are RFCs 1341, 1521, and 1522.

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