In a coexistence scenario, where you’re running Exchange 2007 or Exchange 2010 and Exchange 2013 in the same organization, and your mailbox is still hosted on the Exchange 2007/2010 Mailbox server and you try to access the Exchange 2013 default /ECP directory, you will get the following error:
“Your mailbox can't be accessed using the address you entered, please obtain the correct address, please contact your helpdesk”
To proceed to the control panel you can access the EAC by adding the Exchange version to the URL. For example, to access the EAC whose virtual directory is hosted on the Client Access server locally, use the following URL:
Same way applies if you want to access the Exchange 2010 ECP and your mailbox hosted on an Exchange 2013 Mailbox server, use the following URL:
Through PowerShell create a new mailbox on Exchange 2013 and give it the necessary administrative permissions.