Not all mail system "bounces" go to the correct address.  There are
certain default * FILTER= values that are site-defined when LISTSERV(R)
was installed.  LISTSERV(R) does not like DAEMONs or MAILERs mucking
around sending mail to lists since they "always" represent mail delivery
problems and would very possibly create an email loop.

(Check to see if your lists are cross-linked i.e., one list subscribed to
another.)

/Pete