Thank you for the replies and helpful comments (Pete Weiss, Frank Kuwik
and Mark Williamson). (You were right, Mark!....) When LISTSERV at Buffalo
sent mail for local subscribers it appears the local userids were retained
in some way on the firewall machine and cumulatively added to the next
list to pass through even though they were not a subscriber.  This
accounted for duplicates and the fact that one had to be a listserv list
subscriber to be a 'victim'.  This is the very simple (and not quite
accurate) explanation.  Thanks again!
 
--Trish