We run Exchange 2003 and Outlook 2003. When someone sends a meeting request to one specific user, an NDR is returned to the sender from a user that no longer works here. The original recipient receives the meeting request. This only occurs for one user and only on meeting requests. Regular emails work without an issue. The NDR lists the deleted users x500 name such as /O=email organization/OU=Admin Group/CN=recipients/CN=OldUserName. I have performed an LDAP dump of all x500 and legacy exchange DN but cannot find any reference to the terminated user. Any hints on how to resolve this issue would be appreciated.

Go to the user who receives the meeting request and in Outlook, open up Tools / Options / Delegates. There could be an old delegate listed here that is configured to receive copies of meeting requests sent to the other user.