User receivesb all E-mail, but not from one

We have Windows 2003 w/Exchange 2003 and all service packs on servers are up to date. All users have Windows XP sp2, running Outlook 2003 sp3. Fitz a user receives all E-mail in his inbox except from external user John. I check ESM message history and I can see a delivery of a message from external user John was deposited locally to store to Fitz, but the message from John is no where to be found. Fitz does not have any rules running on his computer. Where is this one E-mail from John going??? Thank you