Usar telnet para chequear conexión POP3

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[root@mail ~]# telnet 192.168.168.2 pop3

Trying 192.168.168.2...

Connected to 192.168.168.2.

Escape character is '^]'.

+OK mail.dominio.com Cyrus POP3 v2.2.12-Invoca-RPM-2.2.12-4.2.cc server ready

LIST

USER usuario

+OK Name is a valid mailbox

PASS prueba

+OK Mailbox locked and ready

LIST

+OK scan listing follows

.

QUIT

+OK

Connection closed by foreign host.