I suggest putting a filter= keyword in your list headers to
exclude the errant gateway from being able to post to the list.
 
Here's the one we CURRENTLY use on TQM-L
 
* Filter= Also,postmaster@*,*@nocmsmgw*,[log in to unmask],*postmstr*@*
 
/Pete ([log in to unmask])
--
Peter M. Weiss         "The 'NET' never naps"             +1 814 863 1843
31 Shields Bldg. -- Penn State Univ -- University Park, PA USA 16802-1202