Most LISTSERV lists' definitions retain the default LISTSERV
feature of PREVENTING the sending of duplicate messages.
 
Once upon a time there was a problem here on PSUVM where
duplicates were being sent, but it did not only involve LISTSERV,
but user-generated e-mail too.  It had to do with (as I recall)
reordering of SMTP queues at the worst possible time.
 
/Pete Weiss,
 Penn State