root@ip-172-31-24-104:/var# telnet itsol.mx 25
Trying 54.186.2.174...
Connected to itsol.mx.
Escape character is '^]'.
Connection closed by foreign host.
root@ip-172-31-24-104:/var# telnet mail.itsol.mx 25
telnet: could not resolve mail.itsol.mx/25: Name or service not known
root@ip-172-31-24-104:/var#