(require 'cl-macs)
(require 'gnus-msg)
(require 'message)

(defun mail-to-many (to subject body)
  (cl-dolist (this-to to)
    (gnus-post-news 'post "")
    (message-goto-to)          (insert this-to)
    (message-goto-subject)     (insert subject)
    (message-goto-body)        (insert body)
    (message-send-and-exit) ))