Microsoft's only supported method of migrating mailboxes directly from Exchange Server 5.5 servers to Exchange Server 2003 servers in an intraorganizational migration is to use the Move Mailbox Wizard. To migrate mailboxes from Exchange 2000 Server servers to Exchange 2003 servers, Microsoft also recommends using the Move Mailbox Wizard, although in-place upgrades are fully supported.
The Move Mailbox Wizard has been around since Exchange 2000, but the Exchange 2003 version is a much more attractive and efficient tool for moving mailboxes from legacy Exchange servers to Exchange 2003. Let's discuss the wizard's use and new features.
When to Use the Wizard
You can use the Move Mailbox Wizard only for intraorganizational migrations, not for interorganizational migrations. In other words, you can use the wizard to move mailboxes only between servers that are within the same Exchange organization. For interorganizational moves, you need to use the Mailbox Merge Wizard (formerly Exmerge) or the Exchange Migration Wizard.
In a mixed-mode organization, the Exchange 2003 Move Mailbox Wizard can move mailboxes only between servers that are within the same Exchange 5.5 site or administrative group. (In a mixed-mode organization, an Exchange 5.5 site corresponds to an Exchange 2003/Exchange 2000 administrative group.) You can move individual or multiple mailboxes between any combination of Exchange 2003, Exchange 2000, and Exchange 5.5 servers. In a native Exchange 2003 or Exchange 2000 organization, you can use the wizard to move mailboxes between servers that are in different administrative groups. In this case, you can move mailboxes between any combination of Exchange 2003 and Exchange 2000 servers.
Because the Exchange 2003 Move Mailbox Wizard is more functional than earlier versions, you can also use it to move mailboxes between Exchange 2000 and Exchange 5.5 servers, even if your environment has no Exchange 2003 servers. To use the wizard in this way, you must first run the Exchange 2003 Forestprep process in your Active Directory (AD) forest. To do so, execute the setup.exe /forestprep command from the \setup\i386 folder on the Exchange 2003 installation CD-ROM. Make sure you run this command on a server in the same Windows domain as your schema operations master server. Then, run Setup again, this time on the server that you'll use as the console for your administrative operations. Choose the option to install only the Exchange Management components. This server only needs to run Windows 2000 (or Windows Server 2003); the server doesn't need to run Exchange or even have it installed. This process installs the Exchange Management Console, which lets you use the Move Mailbox Wizard. You can also install the console on a Windows XP workstation.
How the Wizard Works
The Move Mailbox Wizard makes a Messaging API (MAPI) connection to the source mailbox server, then reads the folder hierarchy from the source server and recreates it on the target server. The wizard initiates a MAPI transfer to move messages from the source server to the target server. If the read of an item fails, the wizard retries the read. If the read fails again, the wizard drops the item from the processing list and either continues processing the mailbox or abandons the processing, depending on your configuration settings, which I discuss later. When the wizard completes a move operation, it removes the contents of the source mailbox from the source server and updates the user's AD object attributes so that the user's mailbox homes on the target server rather than the source server. If you move POP or IMAP users, you might need to update settings on those users' mail clients to point to the mailbox's new server location.
The Exchange 2000 version of the Move Mailbox Wizard is less than perfect in terms of performance and scalability. Although you can use the Microsoft Management Console (MMC) Active Directory Users and Computers snap-in to select multiple user objects, the wizard processes the objects in a strictly sequential fashion. For example, if you select five users, the mailbox move operation for User2 won't begin until the move operation for User1 finishes, and so on.