Office 365 mailbox not showing in Exchange hybrid on-premises

An Exchange hybrid configuration is set up in the organization. When you look in the on-premises Exchange admin center, the Office 365 mailbox is not showing. The mailbox shows only in Office 365. Why is this happening, and what is the solution for Office 365 mailbox not showing in Exchange hybrid on-premises?

Check mailbox in Exchange Online and Exchange on-premises

There is an Office 365 mailbox when you look in Microsoft 365 Exchange admin center. In our example, the user mailbox is Alison Bell with the email address Alison.Bell@exoip.com.

When you check the on-premises Exchange admin center, the mailbox doesn’t show up. Even a search will not show you the mailbox.

Let’s try to find the mailbox with PowerShell. Start Exchange Management Shell as administrator. Run Get-RemoteMailbox cmdlet. You will get the output that the object couldn’t be found.

[PS] C:\>Get-RemoteMailbox -Identity "Alison.Bell@exoip.com"
The operation couldn't be performed because object 'Alison.Bell@exoip.com' couldn't be found on
'DC01-2016.exoip.local'.
    + CategoryInfo          : NotSpecified: (:) [Get-RemoteMailbox], ManagementObjectNotFoundException
    + FullyQualifiedErrorId : [Server=EX01-2016,RequestId=ac7b9c98-6913-4c83-a35c-4351e7308fe4,TimeStamp=6/21/2021 9:2
   5:50 PM] [FailureCategory=Cmdlet-ManagementObjectNotFoundException] 1B6A5890,Microsoft.Exchange.Management.Recipie
  ntTasks.GetRemoteMailbox
    + PSComputerName        : ex01-2016.exoip.local

Why is this happening and what is the solution for Office 365 mailbox not showing in Exchange hybrid on-premises?

Why Office 365 mailbox is not showing in Exchange admin center

The Office 365 mailbox does not show up in Exchange on-premises because:

• You create an on-premises Active Directory user account and assign a license to the mailbox without the Enable-RemoteMailbox cmdlet.
• You create an on-premises Active Directory user account and create the mailbox in Office 365 (cloud) without the Enable-RemoteMailbox cmdlet.

Let’s have a look at how to fix the Office 365 mailbox not showing in Exchange on-premises.

Solution for Office 365 mailbox not showing in Exchange admin center

Run Exchange Management Shell as administrator and run the following three cmdlets.

Step 1. Run Enable-MailUser cmdlet to mail-enable the user that isn’t already mail-enabled.

[PS] C:\>Enable-MailUser -Identity "Alison.Bell@exoip.com" –ExternalEmailAddress "Alison.Bell@exoip365.mail.onmicrosoft.com"

Name            RecipientType
----            -------------
Alison Bell     MailUser

Do you get an error after running the above cmdlet? Read the article ExchangeGuid is mandatory on UserMailbox.

Step 2. Run Enable-RemoteMailbox cmdlet to link the cloud mailbox in the cloud-based service for the existing user in the on-premises Active Directory.

[PS] C:\>Enable-RemoteMailbox "Alison.Bell@exoip.com"

Name            RecipientTypeDetails     RemoteRecipientType
----            --------------------     -------------------
Alison Bell     RemoteUserMailbox        ProvisionMailbox

Step 3. Force sync Azure AD Connect with PowerShell.

PS C:\> Start-ADSyncSyncCycle -PolicyType Delta

Verify Office 365 mailbox showing in Exchange on-premises

Check in the on-premises Exchange admin center that the Office 365 mailbox shows up.

Another check, but this time in Exchange Management Shell. Run Get-RemoteMailbox cmdlet.

[PS] C:\>Get-RemoteMailbox -Identity "Alison.Bell@exoip.com"

Name            RecipientTypeDetails     RemoteRecipientType
----            --------------------     -------------------
Alison Bell     RemoteUserMailbox        ProvisionMailbox

Everything looks great!

Read more: Create Office 365 mailbox in Exchange hybrid »

Conclusion

In this article, you learned why the Office 365 mailbox is not showing in Exchange hybrid on-premises. The solution to this problem is to run both the Enable-MailUser and Enable-RemoteMailbox cmdlets against the on-premises Active Directory user. After that, the Office 365 mailbox shows up in the on-premises Exchange Server.

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