When you say you can access it, how do you mean? Each network service on the server will respond to one or more ports. Telnet is port 23, so if you haven't got it running you can't be too sure that the port is open.
Other connections that you may make could be ftp (port 21) ssh/scp/sftp (port 22) rsh/resh/remsh (port 514) etc.
If you try to telnet to the server, do you:-
- immediately get Connection refused? That sounds like the firewall is open.
- wait for 30 seconds and then get Connection timed out? That sounds like firewall does not allow incoming traffic on port 23.
I hope that this helps, even if it's not actually your problem.
Firewall rules should be denying everything except the specific access they permit to specific IP addresses, hence my concerns for you.
Regards,
Robin