Migration Wizard gives you the option of associating Exchange 2000 mailboxes with accounts on an external domain and of creating new accounts in the external domain.
Note The external domain is always either a Windows NT 4.0 domain or a Windows 2000 domain in a separate forest.
When you migrate your existing mail system to Exchange 2000, there must be an object in Active Directory for every mailbox you migrate. However, you might want to allow accounts on an external domain to access Exchange 2000 mailboxes. When, from Migration Wizard's Account Options, you select Associate with accounts in an external domain, Migration Wizard searches the external domain for a Windows NT 4.0 or Windows 2000 account with a logon identifier (ID) that matches the mailbox ID of the migrating mailbox. Then, one of the following occurs:
The Associate with accounts in an external domain option is helpful when:
A company has a Windows NT 4.0 domain with 100 user accounts. This company installs Exchange 2000 in a new Windows 2000 forest. This company wants to migrate to Exchange 2000 and use the accounts in Windows NT 4.0 to access the new Exchange 2000 mailboxes.
Run Migration Wizard. From the Container For New Windows Accounts screen, select Options. From Account options, select the Associate with accounts in an external domain check box, but do not select the Create new accounts in external domain check box.
Active Directory has 100 disabled accounts to use for Exchange 2000 messaging. Because each disabled account has an association with one of the original Windows NT 4.0 accounts, the external accounts can be used to access the new Exchange 2000 mailboxes.