mail-mode: Newsgroups header ignored

[Dan Jacobson]

Gentlemen, consider what happens in mail-mode when one's buffer only
has a Newsgroups: header,
  Send buffer contents as mail message? (y or n) y
  Sending...
  sendmail-send-it: No recipients

OK, but now add a To: header too. The message sails right through
without having the Newsgroups header acted on appropriately. No news
is posted, no warning given.

At least warn "Why not use message-mode these days, it does all you
want, even adding
   The following message is a courtesy copy of an article
   that has been posted to comp.bla as well.
too."

Indeed, merge mail-mode and message-mode.