The Microsoft Exchange Server Auth Certificate is installed when you install an Exchange Server, and…
Do you have an Exchange hybrid environment, and do you want to convert user mailbox to shared mailbox? That’s possible! But before you do that, check if the mailbox location is in Exchange Online (Microsoft 365/Office 365). If the answer is yes, you have to convert the user mailbox to shared mailbox from on-premises.
We already did write an article about how to convert user mailbox to shared mailbox. Follow the steps in that article if you have an Exchange on-premises environment or an Exchange hybrid environment with mailboxes located on-premises.
Table of contents
Convert user mailbox to shared mailbox
Let’s go through the steps to convert user mailbox to shared mailbox in an Exchange hybrid configuration.
1. Identify Exchange Online mailbox
Run Exchange Management Shell as administrator. Identify that the user mailbox is an Exchange Online mailbox with the Get-RemoteMailbox cmdlet.
[PS] C:\>Get-RemoteMailbox "Test.Mailbox1@exoip.com" Name RecipientTypeDetails RemoteRecipientType ---- -------------------- ------------------- Test Mailbox1 RemoteUserMailbox ProvisionMailbox
Try to run the Get-Mailbox cmdlet, and you will see that the mailbox cannot be found on-premises. Which is correct.
[PS] C:\>Get-Mailbox "Test.Mailbox1@exoip.com" The operation couldn't be performed because object 'Test.Mailbox1@exoip.com' couldn't be found on 'DC01-2016.exoip.local'. + CategoryInfo : NotSpecified: (:) [Get-Mailbox], ManagementObjectNotFoundException + FullyQualifiedErrorId : [Server=EX01-2016,RequestId=6bc6e4f0-8aa5-4a80-a7f4-8755e4af0ac8,TimeStamp=5/16/2021 9:1 0:02 PM] [FailureCategory=Cmdlet-ManagementObjectNotFoundException] E674A159,Microsoft.Exchange.Management.Recipie ntTasks.GetMailbox + PSComputerName : ex01-2016.exoip.local
Let’s have a look at how it looks in on-premises Exchange admin center. As you can see, it’s not possible to convert the Office 365 user mailbox to shared mailbox in on-premises Exchange admin center.
In Microsoft 365 Exchange admin center, you will see the option to convert to shared mailbox in the details pane. When you click on the Convert to Shared mailbox link, it will successfully convert the mailbox to a shared mailbox. But, you should not do that!
Do not convert mailboxes in Microsoft 365 Exchange admin center when you have an Exchange hybrid environment.
The problem is that the on-premises object will still be a user mailbox because it will not write the changes back to the on-premises AD. The on-premises Exchange admin center will show as user mailbox, while in Microsoft 365 exchange admin center it will show as shared mailbox.
2. Run Set-RemoteMailbox cmdlet
Run the Set-RemoteMailbox cmdlet and specify the user mailbox. Make use of the -Type parameter and the Shared value. You can fill in the display name or email address of the mailbox. You will not get an output showing that it’s succeeded after running the cmdlet.
[PS] C:\>Set-RemoteMailbox "Test Mailbox1" -Type Shared [PS] C:\>Set-RemoteMailbox "Test.Mailbox1@exoip.com" -Type Shared
The Shared value is available only in Exchange 2013 CU21 or later, Exchange 2016 CU10 or later, and Exchange 2019. In Exchange 2013 and Exchange 2016, you also need to run setup.exe /PrepareAD. For more information, see KB4133605.
Read more: Install Exchange Cumulative Update »
3. Force sync Azure AD
Force sync Azure AD Connect to have the changes apply to the cloud (Azure AD).
PS C:\> Start-ADSyncSyncCycle -PolicyType Delta
4. Verify converted mailbox type
It’s always good to verify your work. Check that the shared mailbox RecipientTypeDetails object shows the value RemoteSharedMailbox.
[PS] C:\>Get-RemoteMailbox "Test.Mailbox1@exoip.com" Name RecipientTypeDetails RemoteRecipientType ---- -------------------- ------------------- Test Mailbox1 RemoteSharedMailbox ProvisionMailbox, SharedMailbox
Look in on-premises Exchange admin center. The mailbox shows up in the shared mailboxes list. The details pane will show that it’s a Remote shared mailbox.
In Microsoft 365 Exchange admin center, the mailbox shows as Shared mailbox.
Suppose you use the new Microsoft 365 Exchange admin center. Go to Recipients > Mailboxes. Filter on Shared mailbox. It shows the recipient type Shared mailbox.
5. Remove Exchange Online license
The user mailbox most likely has a license because it was a user mailbox. You can remove the Exchange Online license from the shared mailbox. But, before you do that, check if the mailbox size is greater than 50 GB. If the mailbox size is greater than 50 GB, you need to keep the Exchange Online license. Otherwise, you can’t send and receive mail from the shared mailbox.
A user must have an Exchange Online license to access a shared mailbox, but the shared mailbox doesn’t require a separate license. Without a license, shared mailboxes are limited to 50 GB. To increase the shared mailbox size limit to 100 GB, you must assign an Exchange Online Plan 2 license or an Exchange Online Plan 1 license with an Exchange Online Archiving add-on license.
Sign in to Microsoft 365 admin center. Go to Users > Active users. Click on the user and remove or change the license. In our example, we assign Office 365 licenses with Azure group-based licensing, and we need to adjust it from there.
Keep reading: Get shared mailbox size in Office 365 with PowerShell »
In this article, you learned how to convert user mailbox to shared mailbox in Exchange hybrid. Start Exchange Management Shell and run the cmdlet, as seen in the article. After that, verify the recipient type details. It will show as remote shared mailbox.
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