Mailbox type difference in Exchange Hybrid

We see a mailbox with a different mailbox type in Exchange on-premises and Exchange Online. However, the mailbox type should be the same between both organizations in an Exchange Hybrid deployment. Why is that happening, and how to correct this mailbox inconsistency? In this article, you will learn how to fix the mailbox type difference in Exchange Hybrid.

Exchange mailbox type

Let’s look at the info mailbox (info@exoip.com) in both Exchange on-premises and Exchange Online.

The mailbox shows up in Exchange on-premises as a user mailbox.

The mailbox appears in Microsoft 365 Exchange admin center as a shared mailbox.

Why is there an inconsistency between the mailbox in both organizations? Shouldn’t they be the same? Let’s find out more.

Why this happens

The Exchange on-premises server is the authority server. The mailboxes are created from the on-premises organization. That’s why you need to keep at least one Exchange Server on-premises in a hybrid deployment.

In an Exchange Hybrid deployment, you create or edit a mailbox on the Exchange Server on-premises with the options:

• New-RemoteMailbox (Exchange Management Shell)
• Enable-RemoteMailbox (Exchange Management Shell)
• Set-RemoteMailbox (Exchange Management Shell)
• Create Office 365 mailbox (Exchange Admin Center)

If, for example, the info mailbox needs to change from user mailbox to shared mailbox in Exchange Hybrid, you need to convert the mailbox from Exchange Management Shell on-premises. It’s not possible to do that from Exchange admin center on-premises. You set the remote mailbox type to shared. Do you want to set it from shared to a user mailbox? That’s possible. The only difference is that you choose the regular value.

In this case, they didn’t do it as in the above steps. What did happen is that they converted the user mailbox to a shared mailbox in Exchange Online. That’s incorrect, as it will not write the changes back to Exchange on-premises.

So how do you fix it and make the info mailbox in both Exchange organizations the same mailbox type? Let’s look at that in the next step.

Solution for mailbox type difference in Exchange Hybrid

Start Exchange Management Shell as administrator on the on-premises Exchange server or a Management server with the Exchange management tools installed.

Run the Get-RemoteMailbox cmdlet and verify the RecipientTypeDetails for the mailbox. The info mailbox shows as a RemoteuserMailbox.

[PS] C:\>Get-RemoteMailbox "info@exoip.com"

Name     RecipientTypeDetails     RemoteRecipientType
----     --------------------     -------------------
Info     RemoteUserMailbox        ProvisionMailbox

Run the Set-RemoteMailbox cmdlet. Add the Type parameter with the value Shared. It will convert the remote mailbox to a shared mailbox.

[PS] C:\>Set-RemoteMailbox "info@exoip.com" -Type Shared

Verify that everything is set and looks good with the Get-RemoteMailbox cmdlet.

[PS] C:\>Get-RemoteMailbox "info@exoip.com"

Name     RecipientTypeDetails     RemoteRecipientType
----     --------------------     -------------------
Info     RemoteSharedMailbox      ProvisionMailbox, SharedMailbox

Go back to the Exchange admin center on-premises. The mailbox shows as shared. Just like in Exchange Online – Microsoft 365.

Do you want to set the mailbox to a different type? The Type parameter specifies the type of the mailbox. Choose one of the valid values:

• Regular
• Room
• Equipment
• Shared

Read more: Office 365 mailbox not showing in Exchange Hybrid on-premises »

Conclusion

You learned why there is a mailbox type difference in Exchange Hybrid. The solution to the mailbox inconsistency in both Exchange organizations is to set the remote mailbox type from Exchange on-premises.

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