message header
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... header field. However, in no event are headers (either message
headers or body part headers) allowed to contain anything other than
US-ASCII ...
... 8bit", or "binary" is permitted for
the body of a "message/rfc822" entity. The message header fields are
always US-ASCII in any case, and data within the body can still be
...
... message/external-body", it consists of
a header, two consecutive CRLFs, and the message header for the
encapsulated message. If another pair of consecutive CRLFs appears,
...
... encapsulated message. If another pair of consecutive CRLFs appears,
this of course ends the message header for the encapsulated message.
However, since the encapsulated ...
...
The embedded message header fields which appear in the body of the
"message/external-body" data must be used to declare the media type ...