# File lib/rfilter/keyed_mailbox.rb, line 67
    def expire(age)
      cutoff = Time.now - (60 * 60 * 24) * age
      [ File.join(@path, 'new', '*'),
        File.join(@path, 'cur', '*'),
        File.join(@path, '.index', '*')].each { |glob|
        Dir[glob].each { |file|
          File::delete(file) if File::mtime(file) <= cutoff
        }
      }
    end