draft-usefor-article (06) 6.9. Posted-And-Mailed

      Posted-And-Mailed-content = "yes" / "no"

   This header, when used with the "yes" keyword, indicates that the
   article has been both posted to the specified newsgroups and emailed.
   It SHOULD be used when replying to the poster of an article to which
   this one is a followup (see the Mail-Copies-To header in section 6.8)
   and it MAY be used when any article is also mailed to a recipient(s)
   identified in a To and/or Cc header that is also present. The "no"
   keyword is included for the sake of completeness; it MAY be used to
   indicate the opposite state, but is redundant insofar as it only
   describes the default state when this header is absent.

   This header, if present, MUST be included in both the posted and
   emailed versions of the article. The Newsgroups header of the posted
   article SHOULD be included in the email version as recommended in
   section 5.5.  All other headers defined in this standard (excluding
   variant headers, but including specifically the Message-ID header)
   MUST be identical in both the posted and mailed versions of the
   article, and so MUST the body.

        NOTE: This leaves open the question of whether a To or a Cc
        header should appear in the posted version. Naturally, a Bcc
        header should not appear, except in a form which indicates that
        there are additional unspecified recipients.

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