An article MUST have one, and only one, of each of the  fol-
          lowing headers: Date, From, Message-ID, Subject, Newsgroups,
          Path.

               NOTE: MAIL specifies (if read most carefully) that
               there  must be exactly one Date header and exactly
               one From header, but otherwise does  not  restrict
               multiple  appearances  of  headers.   (Notably, it
               permits  multiple   Message-ID   headers!)    This
               appears  singularly  useless,  or even harmful, in
               the context of news, and much current  news  soft-
               ware  will  not  tolerate  multiple appearances of
               mandatory headers.
          Note also that there are situations, discussed in the  rele-
          vant  parts  of  section  6,  where  References,  Sender, or
          Approved headers are mandatory.

          In the discussions of the individual headers, the content of
          each is specified using the syntax notation.  The convention
          used is that the content of, for example, the Subject header
          is defined as <Subject-content>.

5.1. Date
5.2. From
5.3. Message-ID
5.4. Subject
5.5. Newsgroups
5.6. Path