new (TMail::UNIXMbox)

    # File lib/action_mailer/vendor/tmail-1.2.3/tmail/mailbox.rb, line 237
        def initialize( fname, mhdir, readonly, static )
          @filename = fname
          @readonly = readonly
          @closed = false

          Dir.mkdir mhdir
          @real = MhMailbox.new(mhdir)
          @finalizer = UNIXMbox.mkfinal(@real, @filename, !@readonly, !static)
          ObjectSpace.define_finalizer self, @finalizer
        end