At 15:45 6/24/2009 Wednesday, Robert Allen wrote:
>I am the System Admin in charge of a Listserv server.  I have been asked
>to look into a problem that user of one of our lists is experiencing.  The
>user in question will reply to (post) a message to our Listserv and
>receive a "Your message date some date with subject "subject of messag"
>was successfully distributed the XXX List (100 recipients)" message.
>Sometime after that he will receive a "Rejected posting to
>[log in to unmask]<mailto:[log in to unmask]>" message
>basically stating that a message with the same text has all ready been
>posted.  To my knowledge he is not sending the message twice.  Can anyone
>help me?

Have the user display all of the RECEIVED line headers of the correctly distributed as well as the dupicate posting.  Dollars to donuts, some errant MTA is reflecting the distributed post back to the list and LISTSERV correctly intercepts and rejects it back to the purported FROM:

Usually that improperly configured MTA can be IDed and perhaps its specific subscriber.  A SCAN of the subscribers may be necessarily to help pin it down.  Otherwise, and individual explicit email to each subscriber (or forcing a PROBE) should reveal.

/Pete