> One of the lists on our server is sending duplicate messages to
> subscribers. The messages appear in the archives and in subscriber
> mailboxes with identical time and date stamps. I have confirmed in the
> LISTSERV log that it is actually sending the message twice not the SMTP
> server causing the duplicate distribution.

You have a subscriber who's gateway is "reflecting" the message back to
LISTSERV rather than bouncing it according to standards. Looking at the
full headers of the duplicates should give you a clue on who this
subscriber is. You will notice in the archives, each duplicate message has
an additional 6 lines of text. The is the additional received headers
which will point to the offender.