# File bin/experimental-deliver.rb, line 65
def filter_pid(queue_dir)
  pid = nil

  begin
    File::open("Maildir/.filterpid") { |file|
      if Time.now - file.stat.mtime < (60 * 60 * 4)
        pid_str = file.gets.chomp.strip
        if pid_str =~ /^\d+/
          pid = Integer(pid_str)
        end
      end
    }
  rescue Errno::ENOENT
  end
  return pid
end