dropping non-subscriber posts without acknowledgement

The tremendous proportion of spam from non-subscribers has prompted me to attempt
to drop all posts to my mailing list from nonsubscribers, without sending any
acknowledgement at all - to avoid the bounced email multiplication factor.

I have been tinkering with rc.local.s00 in an attempt to do this, but not with very
much success.  I have placed the following at the top of my rc.local.s00 script,
but I find that nothing gets logged to the reject.nosub file, and posts with
attachments from nonsubscribers get matched by recipes further down in this file.
My hope was that if this recipe were matched, that no further processing of the
message would be done, and that it would not be delivered nor rejected.

My testing list does not have foreign_submit set. 

 :0
  * 9876543210^0 foreign_submit ?? y
  * -2^0 ? formail -X"From " -xFrom: -xReply-To: -xSender: -xResent-From: \
           -xResent-Reply-To: -xResent-Sender: -xReturn-Path: | \
           multigram -b1 -m -l$submit_threshold -L$domain \
            -x$listaddr -x$listreq accept accept2

        {
                :0 c
                | formail -i "Subject: ***Aug20 mod drop msg from non-subscriber***"|\
                        $SENDMAIL -oi $maintainer
                :0 A
                reject.nosub
        }

Any assistance is appreciated - thank you in advance.
-- 
Rick DeMattia <[email protected]>
The secret of the universe is|^&*||x|NO CARRIER