We have been trying to track down the problem, to no avail so far.  Here is
what is happening to the best of my knowledge:
 
1. Mailer (lmail) gets a file from listserv.
2. It adds its Received: header and passes it on to SMTP
3. SMTP receives the file, adds its Received: headeru 2d passes it on.
 
THEN STEP 3 OCCURS AGAIN, FREQUENTLY MANY HOURS LATER.
 
What I've been asking for is copies of the headers from each of the
duplications.  Just one set isn't enough.  I need to see the Received:
tags from the duplicates to even have a chance of tracking it.  We've
called the problem in to IBM, but they have no record of this type of
problem with SMTP.