cannot receive mail in Outlook 2000

I have a user who cannot receive external mails from a particular person. The error message that the sender receive is as shown below:

did not reach the following recipient(s):

c=US;a=IBMX400;p=LEVI;o=LSNA;s=Goh;g=Gina;ou1=GHUB;ou2=NA; on Thu, 30
Jun 2005 11:37:53 +0800
The message was undeliverable because the recipient specified in the
recipient postal address was not known at this address
The MTS-ID of the original message is:
c=SG;a=IBMX400;p=LEVI;l=MNLEX1-050630032703Z-5744
sfomsgis1.levi.com 5.1.1

We are using Exchange 2003.

please advise,

thanks and regards,