5xx
例句释义:1.In theory it would be a simple matter to connect to the remote server and test for a 4xx or 5xx response code.理论上，连接到远程服务器并测试4xx或5xx响应代码是件很简单的事。
2.The SMTP error response is a 5xx level protocol response with text that corresponds to the Sender ID status.SMTP错误响应是5xx级协议响应，其文本对应于发件人ID状态。