改写：MX记录允许设置一个优先级，越小的数字代表越高的优先次序。当多个邮件服务器可用时，会根据该值决定投递邮件的服务器。

MX records allow for setting a priority, where a smaller number represents a higher priority. When multiple mail servers are available, the server with the highest priority value will be chosen to deliver the email.