You might want to enable Message Tracking because that might give you some evidence as to whether this e-mail is being received multiple times from outside or received just once and then replicated within the Exchange system. Or you could probably accomplish the same thing by turning up the level of diagnostic logging on the Internet Mail Service (I assume these messages are coming in from an outside source).
Also, I would look closely at the user's mail client (Outlook, I assume?) to seeif any rules have been set up that might cause this behavior by, for example, setting up a forwarding loop. If the Message Tracking shows just one copy coming in and there are no rules to explain the behavior, I would probably run the DS/IS Consistency Adjuster and maybe even a consistency check on the database (offline using eseutil.exe).
If Message tracking shows that multiple copies are being received from outside, it is most likely that the sender has a problem on their end or at an intermediate mail relay server. It is conceivable that a virus could do this or a mail server that is not recognizing that a particular message has been sent and keeps re-sending it.
Best wishes - it's a fascinating problem and one I had not heard of before reading your note.
paul
