Can't remove a remote shared mailbox by using the Exchange admin center on Exchange Server

Summary

This article describes an issue in Exchange hybrid deployments in which administrators can't remove a remote shared mailbox by using the Exchange admin center (EAC) and receive an error that the mailbox isn't a mailbox user. The issue occurs because EAC uses the Remove-Mailbox PowerShell cmdlet, which can't locate the remote shared mailbox object. As a workaround, remove the mailbox by running the Remove-RemoteMailbox cmdlet in Exchange Management Shell (EMS).

Symptoms

In an Exchange hybrid deployment, when you try to remove a remote shared mailbox by using the Exchange admin center (EAC) in Exchange Server, you receive the following error message:

<Mailbox_name> isn't a mailbox user.

Cause

This issue occurs because the EAC attempts to use the Remove-Mailbox cmdlet to remove the mailbox, but this cmdlet is unable to find the specified mailbox object. This behavior can be verified by checking the logs for the commands that were run.

Workaround

To remove the remote shared mailbox, run the Remove-RemoteMailbox cmdlet in Exchange Management Shell instead.