Jim,
 
I'm not surprised that LISTSERV could not detect that mail as an error
message.  It is not from anything recognizable as a mailer daemon and
does not contain anything else to trigger any of LISTSERV's error
message detection code.  I would suggest that you SERVE ... OFF the
address returning the error ([log in to unmask]).  That should prevent the
loop from continuing.
 
Mark R. Williamson, Rice U., Houston TX; [log in to unmask] or @RICEVM1