Shared mailboxes are unexpectedly converted to user mailboxes

TankSupport 41 Reputation points

We are Fully Hybrid setup but all our mailboxes are on O365. We create a remote mailbox from exchange 2010 and convert to shared from EXO.

We have noticed 10 shared mailboxes are automatically convert to user mailbox?

I just convert back to shared using EXO. But what is the fix?

Microsoft Exchange Hybrid Management
Microsoft Exchange Hybrid Management
Microsoft Exchange: Microsoft messaging and collaboration software.Hybrid Management: Organizing, handling, directing or controlling hybrid deployments.
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Accepted answer
  1. Lydia Zhou - MSFT 2,371 Reputation points Microsoft Employee


    This issue my be caused if the RemoteRecipientType attribute is set incorrectly. If you just convert it back to shared mailboxes, the mailboxes may revert to regular mailboxes again the next time that directory synchronization runs.
    We have to modify the RemoteRecipientType use the following command:

    Set-ADUser -Identity ((Get-Recipient PrimarySmtpAddress).samaccountname) -Replace @{msExchRemoteRecipientType=100;msExchRecipientTypeDetails=34359738368}  

    You can check this article for more details: Shared mailboxes are unexpectedly converted to user mailboxes after directory synchronization runs in an Exchange hybrid deployment.

    If the response is helpful, please click "Accept Answer" and upvote it.
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  1. Andy David - MVP 138.6K Reputation points MVP

    In 2013 and above you can create remote mailboxes as shared:

    In Exch 2010, that is not possible, so you have to convert once they are in Exchange Online. I suspect once they sync, they are set set to user mailboxes, so you have to convert to shared and thats what you are seeing.