(forward-line -1)
(while (re-search-backward "^X-Gnus-Newsgroup: " nil t)
(delete-region (point) (progn (forward-line 1) (point))))
(forward-line -1)
(while (re-search-backward "^X-Gnus-Newsgroup: " nil t)
(delete-region (point) (progn (forward-line 1) (point))))