Hybrid deployments are supported only for the current (N) and previous (N-1) Cumulative Updates (CUs). Therefore, all queries for that SMTP address fail. In this situation, the on-premises Exchange environment has no object to reference for the shared mailbox. These issues can occur if the shared mailbox is created by using the Exchange Online management tools. Users can't send mail to the shared mailbox.Users can't view free/busy information for the shared mailbox.Users can't open the shared mailbox in Outlook.In this scenario, you experience one or more of the following issues: You assign Full Access permissions to one or more users.You create a shared mailbox directly in Exchange Online.

You have a hybrid deployment of on-premises Microsoft Exchange Server and Microsoft Exchange Online in Microsoft 365.For more information, see Microsoft 365 Hybrid Configuration wizard for Exchange 2010. Instead, use the Microsoft 365 Hybrid Configuration wizard. Therefore, you should no longer use the old Hybrid Configuration wizard. The Hybrid Configuration wizard that's included in the Exchange Management Console in Microsoft Exchange Server 2010 is no longer supported.

Open shared mailbox owa