It is my understanding that for most standard list
configurations, LISTSERV will NOT generate duplicates
by rejecting attempts at posting a dup.  Nevertheless
those mechanisms can be faked out, either accidentally
or perhaps maliciously.
 
With that said, it is certainly possible that an
SMTP client could generate a duplicate post for
any one of a number of reasons.  That, in and of
itself, is not a LISTSERV problem, and usually
occurs in the final stages of delivery.
 
--  co-owner:   INFOSYS, TQM-L, CPARK-L, ERAPPA-L, JANITORS, LDBASE-L, et -L
URL:mailto:[log in to unmask]                "I get paid by the millisecond"