Symptoms
In Microsoft Office 365 Dedicated/ITAR (vNext), customers experience symptoms that may include, but are not limited to, the following:
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Can't complete AutoDiscover, or a general inability to connect to a user's mailbox
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Inconsistent mail flow, depending on where the message is originated
Cause
This issue occurs if a mailbox is provisioned in both the legacy Exchange Online Dedicated environment and the Exchange Online Dedicated vNext environment.
Resolution
To resolve this issue, use one of the following high-level methods, depending on which mailbox (legacy or vNext) the customer wants to keep active.
Scenario 1: Keep the legacy mailbox, and deprovision the vNext mailbox
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Export the contents of the vNext mailbox. To do this, follow these steps:
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Generate an eDiscovery search. To do this, see In-Place eDiscovery.
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Export the eDiscovery search to PST. To do this, see Export eDiscovery search results to a PST file.
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Remove the license for the customer's vNext mailbox. To do this, use one of the following methods:
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Office365 Portal: Assign or remove licenses for Office 365 for business
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PowerShell: Remove licenses from user accounts with Office 365 PowerShell
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If using group-based licensing:
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Remove the user from the group
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If Dynamic Group is used, ensure user does not match criteria so that user can be removed. This may require modification of the rules, which must be done carefully as it can affect all other members of the group.
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Previously, Microsoft had to clear msExchPreviousHomeMDBSL and msExchPreviousMailboxGuid Active Directory attributes from the vNext user object. This can now be done through self-service. Please refer to the following article to perform this step:
Permanently Clear Previous Mailbox Info -
Provide the PST file to the end user to import by using the Outlook client. To do this, see Import email, contacts, and calendar from an Outlook .pst file.
Scenario 2: Keep the vNext mailbox, and deprovision the legacy mailbox
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Take a PST export of the legacy mailbox to import to the user’s vNext mailbox. You can do this through Outlook or the Office 365 PST import service:
Outlook: Import email, contacts, and calendar from an Outlook .pst file
Office 365 PST Import Service: Overview of importing PST files and SharePoint data to Office 365 -
Contact Microsoft to assist in manually deprovisioning the duplicate mailbox.
