filter (RFilter::DeliveryAgent)

    # File lib/rfilter/delivery_agent.rb, line 199
        def filter(*command)
          log(2, "Action: filter through #{command.inspect}")
          msg = nil
          status = deliver_filter(@message, *command) { |io|
            msg = RMail::Parser.new.parse(io)
          }
          if status != 0
            m = format("filter failed for command %s (status %s)",
                       command.inspect, status.inspect)
            log(1, "Error: " + m)
            raise DeliveryCommandFailure.new(m, status)
          end
          @message = msg
        end