Unable to access Exchange Equipment mailbox with EWS
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I have setup an Office365 equipment mailbox, so that I can open it in outlook (using Open->Other User's Mailbox), but I am unable to access the mailbox using the C# EWS api.
Code to access the mailbox:

    _service.ImpersonatedUserId = new ImpersonatedUserId(ConnectingIdType.SmtpAddress, delegateBox);
     _inbox = Folder.Bind(_service, WellKnownFolderName.Inbox);

The result is the following exception:

    Exception in ProcessWebException
    Microsoft.Exchange.WebServices.Data.ServiceResponseException: The SMTP address has no mailbox associated with it.
    at Microsoft.Exchange.WebServices.Data.ServiceRequestBase.ProcessWebException(WebException webException)
    at   Microsoft.Exchange.WebServices.Data.ServiceRequestBase.GetEwsHttpWebResponse(HttpWebRequest request)
    at Microsoft.Exchange.WebServices.Data.SimpleServiceRequestBase.InternalExecute()
    at Microsoft.Exchange.WebServices.Data.MultiResponseServiceRequest`1.Execute()
    at Microsoft.Exchange.WebServices.Data.ExchangeService.BindToFolder(FolderId folderId, PropertySet propertySet)
    at Microsoft.Exchange.WebServices.Data.ExchangeService.BindToFolder[TFolder](FolderId folderId, PropertySet propertySet)
    at Microsoft.Exchange.WebServices.Data.Folder.Bind(ExchangeService service, WellKnownFolderName name)