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@ -593,37 +593,43 @@ interoperability issues result from it:
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{{RFC2046}} on "Multipart Media Type). In the following an excerpt
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of paragraphs that may be relevant in this context:
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> A body part is an entity and hence is NOT to be interpreted as
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> actually being an RFC 822 message. To begin with, NO header fields
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> are actually required in body parts. A body part that starts with a
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> blank line, therefore, is allowed and is a body part for which all
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> default values are to be assumed. In such a case, the absence of a
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> Content-Type header usually indicates that the corresponding body has
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> a content-type of "text/plain; charset=US-ASCII".
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>
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> The only header fields that have defined meaning for body parts are
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> those the names of which begin with "Content-". All other header
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> fields may be ignored in body parts. Although they should generally
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> be retained if at all possible, they may be discarded by gateways if
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> necessary. Such other fields are permitted to appear in body parts
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> but must not be depended on. "X-" fields may be created for
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> experimental or private purposes, with the recognition that the
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> information they contain may be lost at some gateways.
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>
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> NOTE: The distinction between an RFC 822 message and a body part is
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> subtle, but important. A gateway between Internet and X.400 mail,
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> for example, must be able to tell the difference between a body part
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> that contains an image and a body part that contains an encapsulated
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> message, the body of which is a JPEG image. In order to represent
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> the latter, the body part must have "Content-Type: message/rfc822",
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> and its body (after the blank line) must be the encapsulated message,
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> with its own "Content-Type: image/jpeg" header field. The use of
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> similar syntax facilitates the conversion of messages to body parts,
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> and vice versa, but the distinction between the two must be
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> understood by implementors. (For the special case in which parts
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> actually are messages, a "digest" subtype is also defined.)
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{::include ../shared/fence-line.mkd}
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A body part is an entity and hence is NOT to be interpreted as
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actually being an RFC 822 message. To begin with, NO header
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fields are actually required in body parts. A body part that
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starts with a blank line, therefore, is allowed and is a body
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part for which all default values are to be assumed. In such a
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case, the absence of a Content-Type header usually indicates
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that the corresponding body has a content-type of "text/plain;
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charset=US-ASCII".
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The only header fields that have defined meaning for body parts
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are those the names of which begin with "Content-". All other
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header fields may be ignored in body parts. Although they
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should generally be retained if at all possible, they may be
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discarded by gateways if necessary. Such other fields are
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permitted to appear in body parts but must not be depended on.
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"X-" fields may be created for experimental or private purposes,
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with the recognition that the information they contain may be
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lost at some gateways.
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NOTE: The distinction between an RFC 822 message and a body part
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is subtle, but important. A gateway between Internet and X.400
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mail, for example, must be able to tell the difference between a
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body part that contains an image and a body part that contains
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an encapsulated message, the body of which is a JPEG image. In
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order to represent the latter, the body part must have
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"Content-Type: message/rfc822", and its body (after the blank
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line) must be the encapsulated message, with its own
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"Content-Type: image/jpeg" header field. The use of similar
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syntax facilitates the conversion of messages to body parts, and
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vice versa, but the distinction between the two must be
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understood by implementors. (For the special case in which
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parts actually are messages, a "digest" subtype is also
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defined.)
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{::include ../shared/fence-line.mkd}
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The MIME structure of an Email message looks as follows:
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