    # File lib/action_mailer/vendor/tmail-1.2.3/tmail/mailbox.rb, line 427
        def new_port
          fname = nil
          tmpfname = nil
          newfname = nil

          begin
            fname = "#{Time.now.to_i}.#{$$}_#{Maildir.unique_number}.#{Socket.gethostname}"

            tmpfname = "#{@tmp}/#{fname}"
            newfname = "#{@new}/#{fname}"
          end while FileTest.exist? tmpfname

          if block_given?
            File.open(tmpfname, 'w') {|f| yield f }
            File.rename tmpfname, newfname
            PORT_CLASS.new(newfname)
          else
            File.open(tmpfname, 'w') {|f| f.write "\n\n" }
            PORT_CLASS.new(tmpfname)
          end
        end