Exchange server 5.5

I migrate my WinNt4.0 PDC to Win2000 server as domain controller.
After I migrate users and groups successfully. It came to my attention that all users can not retrieve their E-mails, then I noticed that my WinNT4.0 Exchange 5.5 sever is not working with my new active directory.
Is there anything that I have to do to make my Exchange 5.5 work with my new Active Directory?