RFC977 3.4.1.  IHAVE

   IHAVE <messageid>

   The IHAVE command informs the server that the client has an article
   whose id is <messageid>.  If the server desires a copy of that
   article, it will return a response instructing the client to send the
   entire article.  If the server does not want the article (if, for
   example, the server already has a copy of it), a response indicating
   that the article is not wanted will be returned.

   If transmission of the article is requested, the client should send
   the entire article, including header and body, in the manner
   specified for text transmission from the server. A response code
   indicating success or failure of the transferral of the article will
   be returned.

   This function differs from the POST command in that it is intended
   for use in transferring already-posted articles between hosts.
   Normally it will not be used when the client is a personal
   newsreading program.  In particular, this function will invoke the
   server's news posting program with the appropriate settings (flags,
   options, etc) to indicate that the forthcoming article is being
   forwarded from another host.

   The server may, however, elect not to post or forward the article if
   after further examination of the article it deems it inappropriate to
   do so.  The 436 or 437 error codes may be returned as appropriate to
   the situation.

   Reasons for such subsequent rejection of an article may include such
   problems as inappropriate newsgroups or distributions, disk space
   limitations, article lengths, garbled headers, and the like.  These
   are typically restrictions enforced by the server host's news
   software and not necessarily the NNTP server itself.

RFC977 3.4.2.  Responses

   235 article transferred ok
   335 send article to be transferred.  End with <CR-LF>.<CR-LF>
   435 article not wanted - do not send it
   436 transfer failed - try again later
   437 article rejected - do not try again

   An implementation note:

   Because some host news posting software may not be able to decide
   immediately that an article is inappropriate for posting or
   forwarding, it is acceptable to acknowledge the successful transfer
   of the article and to later silently discard it.  Thus it is
   permitted to return the 235 acknowledgement code and later discard
   the received article.  This is not a fully satisfactory solution to
   the problem.  Perhaps some implementations will wish to send mail to
   the author of the article in certain of these cases.