Disable User Access to the New Outlook for Windows with Owa Mailbox Policy does not work

Question

Hi,

we want to block access to the new Outlook for Windows with a "Owa Mailbox Policy" as described in the official MS documentation https://learn.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/outlook-on-the-web/enable-disable-employee-access-new-outlook#step-2-use-the-set-owamailboxpolicy-cmdlet-to-enable-or-disable-access-to-work-or-school-mailboxes-in-outlook-for-windows

We have around 3.000 employees, who at least already have tested or configured the New Outlook for Windows, which we want to prevent now with a Owa Mailbox Policy.

First, we tested the settings mentioned in the above article for single users who are already using the new Outlook or wanted to configure the New Outlook for the first time with the Set-CASMailbox -Identity @****.com -OneWinNativeOutlookEnabled $false.

This has been working and the access to the New Outlook is blocked for both, new and existing new Outlook users.

In the second step, we created a custom "Owa Mailbox Policy" with the setting -OneWinNativeOutlookEnabled $false, assigned the policy to the same users and reverted the value for Set-CASMailbox -Identity @**.com -OneWinNativeOutlookEnabled back to $True.

Now, even after waiting for 5 days, the Owa Mailbox policy still does not block the access for users, who already have been using the New outlook.

Is there anything we are missing here? Or is the rollout of MC922623 still not complete to achieve the above mentioned scenario?

Thank you

Answer 1

Hello @Hauff, Thomas (Bilfinger Global IT GmbH),

Thank you for posting your question in the Microsoft Q&A forum.   

Before providing further troubleshooting steps, can you confirm some information about: 

1. What is the version of PowerShell that you’re using? 
2. Did you check if you've successfully applied an Outlook on the web mailbox policy to a mailbox?  

To verify that you've applied a mailbox policy to a mailbox for Outlook on the web and the new Outlook for Windows, perform any of the following steps: 

• In the Exchange Admin Center, go to Recipients > Mailboxes and select the mailbox. In the Details flyout that opens, select Manage email apps settings under Email apps & mobile devices, and verify the name of the policy in the Outlook web app mailbox policy box. 
• In Exchange Online PowerShell, replace <MailboxIdentity> with the name, alias, email address, or account name of the mailbox, and run the following command to verify the value of the OwaMailboxPolicy property: 

Get-CasMailbox -Identity "<MailboxIdentity>" | Format-List OwaMailboxPolicy `` 

• In Exchange Online PowerShell, run the following command to verify the value of the OwaMailboxPolicy property for all mailboxes: 

Get-CasMailbox -ResultSize unlimited | Format-Table Name,OwaMailboxPolicy –Auto 

3. Did you check if the custom Owa Mailbox Policy is actually assigned to the affected users? You can used this PowerShell code to check for their policy assignment: 

Get-CASMailbox -Identity ******@domain.com | Select OwaMailboxPolicy  

If the output shows a different policy than the one you configured with   OneWinNativeOutlookEnabled  $false, then the user is not assigned correctly. 

This information will help me understand the issue better and provide you with further accurate troubleshooting steps. 

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