MIME discrete media types allow MIME to represent hundreds of different kinds of data in e-mail messages. This alone would make MIME an incredibly useful technology, but the MIME standard goes one step further, by defining composite media types. These allow MIME to perform even more “spectacular feats”, such as sending many types of data at once, or encapsulating other messages or information into e-mail.

The use of a MIME composite media type is indicated via the Content-Type header of an RFC 822 message. Instead of one of the six discrete media types (text, image, audio, video, model and application), one of these two composite media types is used:

• Multipart Media Type (multipart): Allows one or more sets of data to be sent in a single MIME message. Each piece of data is represented as an individual discrete media type.
  
  
• Message Media Type (message): Allows a message to encapsulate another message. This may be another e-mail message previously sent, or a message of some other kind. This media type also provides flexibility for sending partial messages and other special types of communication.