In a Microsoft Exchange Server environment, the move-mailbox process may cause data loss. This problem may occur when you move mailboxes in complex environments that have multiple Active Directory sites and multiple Exchange servers.

During the move-mailbox process, a destination mailbox is created so that data can be copied to it. This destination mailbox is not yet associated with a user account. The process by which a destination mailbox is associated with a user account does not occur until all contents have been copied to the destination mailbox. During the final step of the move-mailbox process, the user attributes are updated to point to the new server and to the new database. The destination mailbox is associated with the user account during this attribute-updating process.

This issue occurs because online maintenance identifies mailboxes that are past their retention dates and then deletes them. As part of this task, online maintenance runs a cleanup agent that identifies disconnected or reconnected mailboxes. If the cleanup agent is run on the destination mailbox store during a move process, the destination mailbox is identified as disconnected. In some cases, the destination mailbox is purged because the cleanup agent is run from a destination Exchange server that is pointing at a different Active Directory site, and the Exchange attributes (homeMDB, homeMTA, and msExchHomeServerName) have not yet been updated. In this scenario, the cleanup agent detects that the mailbox is not attached to a user account. If the mailbox is past the retention date in this situation, the mailbox is deleted. This causes problems because the source mailbox is also deleted after a successful move-mailbox operation.

To resolve this issue, use one of the following methods:

• Set the deleted mailbox retention period to a nonzero value on the destination mailbox server. By default, this retention period is 30 days. For more information about how to configure the deleted mailbox retention period, visit the following Microsoft Web site:
  http://technet.microsoft.com/en-us/library/bb125047.aspx (http://technet.microsoft.com/en-us/library/bb125047.aspx)
• Configure the online maintenance interval so that it does not overlap the scheduled move-mailbox operation. Or, do not run online maintenance for the mailbox store during the day or days on which you want to move the mailbox. For more information about how to configure the Exchange database online maintenance schedule, visit the following Microsoft Web site:
  http://technet.microsoft.com/en-us/library/aa995705.aspx (http://technet.microsoft.com/en-us/library/aa995705.aspx)

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

If you delete a mailbox in Microsoft Exchange 2000 Server or in Microsoft Exchange Server 2003, the mailbox is not immediately deleted. Instead, it is marked as disconnected. If the mailbox is disconnected, and the retention period has expired, the mailbox is deleted.