Claudia,
  I've learned the hard way -- insist that subscribers send you at least
two headers off the messages they're complaining about. Otherwise, there's
no way to tell what's going on. There are lots of possibilities and it's
hard to track them down without the mail headers. In your case, I'd ask
the subscriber to forward to you the entire message, both copies received,
including the headers.
 
Valorie King
TAGFAM
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