Execute command:
telnet smtp.exmail.qq.com 465
Information appears:
[root@pengman Desktop]# telnet 10.223.30.128 7027
Tring 10.223.30.128.7027
Connected to 10.223.30.128 (10.223.30.128) // indicates a successful connection
Escape character is '^]' // Not an error, the ^ in "^]" means ctrl key, which means press Ctrl and ] keys at the same time to enter the command mode of telnet client.
Connection closed by foreign host. // If there is no other command data input for a long time, linux will automatically close the corresponding connection.