Use a SOAP exception to handle errors that occur on the client side during the generation of the SOAP request or the unmarshalling of the response.
Use a SOAP fault to handle errors that occur on the server side when unmarshalling the request, processing the message, or marshalling the response. In response to such an error, server-side code should create a SOAP message that contains a fault element, rather than a body element, and then it should send that SOAP message back to the originator of the message. If the message receiver is not the ultimate destination for the message, it should identify itself as the soapactor so that the message sender knows where the error occurred. For additional information, see Handling SOAP Faults.