code: @Override
      protected Message createSubmitFaxJobMessage(FaxJob faxJob,MailResourcesHolder mailResourcesHolder)
      {
          //set from
          String from=faxJob.getSenderEmail();
          if((from==null)||(from.length()==0))
          {
              throw new FaxException("From address not provided.");
          }
          
          //create message
          Message message=super.createSubmitFaxJobMessage(faxJob,mailResourcesHolder);
          
          return message;
      }
docs: This function will create the message used to invoke the fax
  job action.<br>
  If this method returns null, the SPI will throw an UnsupportedOperationException.
  
  @param   faxJob
  The fax job object containing the needed information
  @param   mailResourcesHolder
  The mail resources holder
  @return  The message to send (if null, the SPI will throw an UnsupportedOperationException)