instance method update

# File actionmailer/lib/action_mailer/vendor/tmail-1.2.7/tmail/mailbox.rb, line 335
    def update
      return if FileTest.zero?(@filename)
      return if @updated and File.mtime(@filename) < @updated
      w = nil
      port = nil
      time = nil
      UNIXMbox.lock(@filename) {|f|
          begin
            f.each do |line|
              if /\AFrom / === line
                w.close if w
                File.utime time, time, port.filename if time

                port = @real.new_port
                w = port.wopen
                time = fromline2time(line)
              else
                w.print line if w
              end
            end
          ensure
            if w and not w.closed?
              w.close
              File.utime time, time, port.filename if time
            end
          end
          f.truncate(0) unless @readonly
          @updated = Time.now
      }
    end