In DW I clicked on the Contact: Basic Default form tab then on Properties clicked on Edit Form. In the Form Content tab I set Persistence to Session since it always defaults to None. Then in the Form Function tab I clicked on the To: field and typed in ,firstname.lastname@example.org. This did not send.
Next, in the same file with two addresses I deleted the second address using Code View. (I always hate to do this in DW since I have to detach the template from the file.) The single address does not send either. Latest file attached