155: Why doesn't Gnus generate the "Lines:" header?

  The posting software down the line from Gnus often generates a "Lines:"
  header so Gnus doesn't have to.  If you want it to, just add Lines to the
  list in gnus-required-headers:

    (add-hook 'gnus-startup-hook
        '(lambda ()
           (setq gnus-required-headers (cons 'Lines gnus-required-headers))))