Office 365 Migrations – Helpful Tips (2)

In part two of this series on migrating mailboxes to Office 365, I want to explore a situation that my client experience with mailboxes that migrated, but were not acting properly. The scenario is the client had Exchange 2003 SP2 on-prem. We put in the usual full monty of ADFS, DirSync, and a Hybrid Exchange 2010 server. Once all these pieces were in place we began migrations on a site to site basis.

On to the migration!
One of these sites did not go as planned. We experienced multiple errors that eventually led us down the path to Active Directory replication issues. Our error messages were as follows:

  • MapiExceptionMailboxDisabled: Unable to open message store. (hr=0x80004005, ec=2412)
  • MapiExceptionWrongServer: Unable to open mailbox “” on server “”. (hr=0x80004005, ec=1144)
  • Source user ” doesn’t have a primary mailbox.
  • MapiExceptionUnknownUser: Unable to open message store. (hr=0x80004005, ec=1003)

After a bit of research and a bit of digging into the Active Directory we found we had strong replication enabled partially Active Directory issues and Lingering Objects. We were able to clean this issues following links like this:

Another Issue Crops Up
Once Active Directory was clean we was able to move the mailboxes to the cloud without any errors. However, and we should have expected this, there were ‘remnants’ still visible in Active Directory/Exchange. When we opened up the Exchange Management Console and saw that the mailboxes were listed as Remote Mailboxes:


So why is this bad? Once the mailbox is moved to the cloud, they should not appear in this console at all. On the client side, Outlook does not redirect to the Office 365 servers. Also mail flow stops. What’s the solution to this?

The Fix
First we need to disable the on-prem mailbox:

Disable-mailbox [user alias]

Then we need to enable the remote-mailbox for the cloud:

Enable-RemoteMailbox [user alias] -RemoteRoutingAddress

Once the commands are completed, the Remote Mailbox entries in the Exchange EMC are no longer present. Now your Outlook client will connect to the mailbox after it is redirected to the Office 365 Exchange servers.

Next in the series
The third part of this series will look at what happens to some mailboxes that needed the above fix and now have issues in the cloud.


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