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