# File lib/action_mailer/vendor/tmail-1.2.3/tmail/mailbox.rb, line 52
    def initialize( dir )
      edir = File.expand_path(dir)
      raise ArgumentError, "not directory: #{dir}"\
                              unless FileTest.directory? edir
      @dirname = edir
      @last_file = nil
      @last_atime = nil
    end