# File lib/rfilter/delivery_agent.rb, line 321
      def exitcode(exception)
        case exception
        when DeliverySuccess
          RFilter::MTA::EXITCODE_DELIVERED
        when DeliveryReject
          RFilter::MTA::EXITCODE_REJECT
        when DeliveryComplete
          RFilter::MTA::EXITCODE_DEFER
        else
          raise ArgumentError,
            "argument is not a DeliveryComplete exception: " +
            "#{exception.inspect} (#{exception.class})"
        end
      end