Telnet is a fantastic troubleshooting tool that has not lost it's place in the support world.You can test a connection to your mailserver by using telnet. To test if you can connect to SMTP (outbound) port type;

telnet 25

We'll try gmails mail server;

-bash-3.00# telnet 25
Connected to
Escape character is '^]'.
220 ESMTP g1si6939040rvb

Now type 'ehlo' (w/o the quotes) to make sure the mail server is functioning properly.

ehlo at your service, []
250-SIZE 28311552

To break out of a telnet connection press 'CNTRL ]' (the control key plus the right bracket) then type quit;

telnet> quit
Connection closed.

Now to test your POP3 (incoming) mail server;

-bash-3.00# telnet 110
Connected to
Escape character is '^]'.
+OK Hello there.
USER sentinal
+OK Password required.
PASS (H@Lo-3)
+OK logged in.
+OK POP3 clients that break here, they violate STD53.
1 1120

The line "1 1120" means that I have one message. To view the message type 'RETR 1'. You can also delete a message by typing 'DELE 1'. Type 'QUIT' to exit.