Exchange 2000 Lost E-mail address

I have an Exchange 2000 native system that was an upgrade from a 5.5 domain. Windows 2000 is still mixed domain. I am trying to assign an e-mail address to a user and the system tells me “This e-mail address already exists in this organization. ID c10312e7 Microsoft Active Directory – Exchange Extension” I have tried the methods Microsoft suggests with no results. Does anyone know how I can find out where in AD that that password is? I can send mail to it and it does not bounce back so it is someplace in the system. Thanks