Users in a hybrid deployment can't access a shared mailbox that was created in Exchange Online
The Hybrid Configuration wizard that's included in the Exchange Management Console in Microsoft Exchange Server 2010 is no longer supported. Therefore, you should no longer use the old Hybrid Configuration wizard. Instead, use the Microsoft 365 Hybrid Configuration wizard. For more information, see Microsoft 365 Hybrid Configuration wizard for Exchange 2010.
Consider the following scenario:
- You have a hybrid deployment of on-premises Microsoft Exchange Server and Microsoft Exchange Online in Microsoft 365.
- You create a shared mailbox directly in Exchange Online.
- You assign Full Access permissions to one or more users.
In this scenario, you experience one or more of the following issues:
- Users can't open the shared mailbox in Outlook.
- Users can't view free/busy information for the shared mailbox.
- Users can't send mail to the shared mailbox.
These issues can occur if the shared mailbox is created by using the Exchange Online management tools. In this situation, the on-premises Exchange environment has no object to reference for the shared mailbox. Therefore, all queries for that SMTP address fail.
Hybrid deployments are supported only for the current (N) and previous (N-1) Cumulative Updates (CUs). If you're running Exchange Server 2013 (CU20 or earlier versions) or Exchange Server 2016 (CU9 or earlier versions), it is important that you upgrade to the latest version to protect your server's integrity.
For on-premises environments that use Exchange Server 2013 (CU21 or later versions) or Exchange Server 2016 (CU10 or later versions), do the following:
Create an on-premises object for the cloud mailbox by using the
New-RemoteMailbox cmdlet with the
-Shared switch in Exchange Management Shell.
This object must have the same name, alias, and user principal name (UPN) as the cloud mailbox. For more information, see New-RemoteMailbox.
For example, run the following command:
New-Remotemailbox -Name "<Shared mailbox>" -Alias <sharedmailbox> -UserPrincipalName <email@example.com> -Remoteroutingaddress <firstname.lastname@example.org> -Shared
For more information about remote shared mailboxes, see Shared mailboxes are unexpectedly converted to user mailboxes after directory synchronization runs in an Exchange hybrid deployment and Cmdlets to create or modify a remote shared mailbox in an on-premises Exchange environment.