Outlook Multiple message

Hi all, I have just move over to Outlook 98 as our internal and external email client, using Exchange. This went well, but now I have a problem with emails being received up to 4 times (the same one).

It’s not happening to everyone just one user (The MD, such is life), he gets certain emails from certain people 4 times (the same message 4 times?).

I sent a message from Yahoo and from Hotmail to him to see if the same would happen, but they only came once?

Does anyone have any ideas, he is the only one to have reported the problem.

Setup Client is Win98, Outlook 98 (TCP/IP only)
Server is Win2k Server, Exchange 5.5.

Thanks.

Simon