The agent cannot logon to the System Attendant or other service mailbox.
MAPI access is disabled on the server or at a mailbox level.
Use the Exchange Management Console to enable or disable MAPI for a user mailbox. You need to be assigned permissions before you can perform this procedure. To see what permissions you need, see the "Client Access user settings" entry in the Client Access Permissions topic.
You need to be assigned permissions before you can perform this procedure. To see what permissions you need, see the "Client Access user settings" entry in the Client Access Permissions topic.
This example enables MAPI for the user John.
Set-CASMailbox -Identity John -MAPIEnabled $trueThis example disables MAPI for the user John.
Set-CASMailbox -Identity John -MAPIEnabled $falseFor detailed syntax and parameter information, see Set-CASMailbox.