You may find usernames and passwords for email accounts, so here is how to check the mail using Telnet
root@kali:~# telnet $ip 110
+OK beta POP3 server (JAMES POP3 Server 2.3.2) ready
USER billydean
+OK
PASS password
+OK Welcome billydean
list
+OK 2 1807
1 786
2 1021
retr 1
+OK Message follows
From: [email protected]
Dear Billy Dean,
Here is your login for remote desktop ... try not to forget it this time!
username: billydean
password: PA$$W0RD!Z