How to eliminate Group Reply problem.

I've set up a recipe that basically resends all mail sent to a
particular address to all the addresses that are kept in a separate
file. Also, another file contains a list of administrators that are
allowed to send to the bigger list. Think of it as a one-way mailing
list server.

Anyway, the recipe works fine but has one little quirk: If a recipient
does a "Group Reply", the reply correctly goes to the sender, but also
goes to the sender's domain without a username. Ie., if the message was
sent by "joe(_at_)mydomain(_dot_)com", the group reply sends the reply to
"joe(_at_)mydomain(_dot_)com" and a CC: to "mydomain.com" which generates an 
error
on the local host. 

Here's the recipe. Any clues on how to eliminate this?

=========================
LINEBUF=10000

SENDER=`formail -rtzx To:`

:0
* ^TO.mmembers*
{ 
        :0 h
        * ? test -f $MAILDIR/admin
        * ? fgrep -i -s "$SENDER" $MAILDIR/admin
        { 
        :0
        | formail -I To:"(List Members)" -k -X Reply-To: -X From: -X
Subject:
-X To: -I Apparently-To: | $SENDMAIL -oi `cat $MAILDIR/Mlist` 

        }

        :0 E
        /dev/null
}
==========================

--
        Gary Fischman
        fischman(_at_)nynexst(_dot_)com