Many  MAIL  headers,  and many of those specified in present
          and future MAIL extensions, are  potentially  applicable  to
          news.   Headers  specific to MAIL's point-to-point transmis-
          sion paradigm, e.g. To and Cc, SHOULD  not  appear  in  news
          articles.   (Gateways  wishing  to preserve such information
          for debugging probably SHOULD hide it under different names;
          prefixing  "X-"  to  the original headers, resulting in e.g.
          "X-To", is suggested.)

          The following optional headers are either specific  to  news
          or  of particular note in news articles; an article MAY con-
          tain some or all of them.  (Note that there are some circum-
          stances  in  which  some  of  them  are mandatory; these are
          explained under the individual headers.)   An  article  MUST
          not contain two or more headers with any one of these header
          names.

               NOTE: The ban on duplicate header names  does  not
               apply  to  headers  not specified in this Draft at
               all, such as "X-" headers.   Software  should  not
               assume  that  all  header names in a given article
               are unique.

6.1. Followup-To
6.2. Expires
6.3. Reply-To
6.4. Sender
6.5. References
6.6. Control
6.7. Distribution
6.8. Keywords
6.9. Summary
6.10. Approved
6.11. Lines
6.12. Xref
6.13. Organization
6.14. Supersedes
6.15. Also-Control
6.16. See-Also
6.17. Article-Names
6.18. Article-Updates