MIME Basic Structures and Headers

The creators of the MIME standard had a difficult challenge on their hands: how to bring flexibility in the types of data contained in email messages, when RFC 822 said that messages could contain only ASCII text. To accomplish this, MIME creators had to exploit the areas of flexibility that had already been put into the existing RFC 822.

Two such opportunities were available: The first was the fact that RFC 822 message bodies are allowed to contain any type of ASCII text, as long as lines don't exceed 998 text characters and each line ends with a CRLF control code combination. Even though the creators of RFC 822 naturally assumed this ASCII text would be human-readable, there was nothing stopping it from being ...

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