RFC 4288:Media Type Specifications and Registratio...
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agent


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... For example, a meeting scheduler might define a standard representation for information about proposed meeting dates. An intelligent user agent would use this information to conduct a dialog with the user, and might then send additional material based on that dialog. More generally, there have been several "active ...
... In the asynchronous mail environment, where information on the capabilities of the remote mail agent is frequently not available to the sender ...



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