XADM: Error When Creating a Mailbox for a User That Already Has E-mail Address

When you use the Windows 2000 Active Directory Users and Computers Microsoft Management Console (MMC) snap in to enable or add Exchange 2000 Server mail for a user that is not mailbox-enabled but that does have an SMTP e-mail address defined on the General tab of the user properties, you receive the following error message:

To resolve this issue:

1. Right-click the user object, and then click Disable Exchange Mail.
2. When the warning message of removing all e-mail addresses appears, click Yes to confirm.
3. Right-click the user object, click Enable Exchange Mail or Add Exchange Mail.

This behavior is by design.