The best way to do it:
sendmail junk@thehouse.org < onemessage
or
formail -ds sendmail junk@thehouse.org < manymessages
If you use Emacs and VM, the following code will bind J in the summary
window to do the Right Thing.
(defvar flan-junkmail-address "junk@thehouse.org"
"The address to forward all junkmail to.")
(defun flan-junk-junkmail (prefix-arg)
"Send all junkmail to 'flan-junkmail-address and delete it."
(interactive "p")
(if (interactive-p)
(vm-follow-summary-cursor))
(vm-delete-message 1)
(vm-pipe-message-to-command (concat "/usr/lib/sendmail "
flan-junkmail-address)
prefix-arg))
(define-key vm-mode-map "J" 'flan-junk-junkmail)