UnableToWriteToAadException For Mailbox Stored in Cloud but Managed On-Prem

Ryan Broman 21 Reputation points


I'd like to add an email address to a user like so:

Set-Mailbox RBroman -EmailAddresses @{add="TestRBroman@xyz.com"}  

However, when running it while connected to Exchange Online I get the following error:

An Azure Active Directory call was made to keep object in sync between Azure Active Directory and Exchange Online. However, it failed. Detailed error message:  
        Unable to update the specified properties for on-premises mastered Directory Sync objects or objects currently undergoing migration. DualWrite (Graph) RequestId:   

We are a hybrid environment and recently moved our mailboxes to the cloud. So I opened Exchange Management Shell on-prem to try it and received a Not Found Error:

The operation couldn't be performed because object 'rbroman' couldn't be found on ''.  

So if I can't edit mailboxes in the cloud AND I can't edit them on-prem, what do I do?

It should be noted that I am able to edit the mailbox using the on-prem EAC but am trying to automate processes via PowerShell.

Windows 365 Business
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Accepted answer
  1. Andy David - MVP 145.1K Reputation points MVP

    on-prem its a remote mailbox

    Set-RemoteMailbox RBroman -EmailAddresses @{add="TestRBroman@xyz.com"}

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