Identify Resource Mailboxes
A primary mailbox is the mailbox where a user receives mail, whereas a nonprimary (or resource) mailbox is a mailbox created for resources such as conference rooms or group mailboxes. Resource mailboxes are owned by users who also own a primary mailbox.
In Exchange 2000, a mailbox is an attribute of an object in Active Directory, not an object itself. Therefore, each user object in Active Directory can only be matched to one mailbox, which is the user's primary mailbox.
Resource mailboxes become separate objects in Active Directory during the migration process. For this reason, resource mailboxes must be identified before running Migration Wizard so that Migration Wizard handles them differently than primary mailboxes. Migration Wizard identifies resource mailboxes that are to be migrated by searching for the value NTDSNoMatch in each resource mailbox's custom attributes. For this reason, if a user has a primary mailbox and one or more resource mailboxes, all mailboxes but the primary mailbox must be stamped with the value NTDSNoMatch.
Important Migration Wizard will only migrate multiple mailboxes that are associated with the same user if all but one of the mailboxes are stamped with the value NTDSNoMatch.
You can identify a resource mailbox manually by typing the value NTDSNoMatch in any of the resource mailbox's 15 custom attributes. Or, you can identify resource mailboxes automatically by running the NTDSNoMatch Utility. The NTDSNoMatch Utility is included with Exchange 2000 Service Pack 1 (SP1) and must be run on a Windows 2000 computer. For more information about the NTDSNoMatch Utility, consult Microsoft Knowledge Base article Q274173, "XADM: Documentation for the NTDSNoMatch Utility."