If iptables is not running (to be more precise: the kernel module is unloaded [ /etc/init.d/iptables stop]) and it still does not work:
The iptables script just instantiates or removes a set of rules, it doesn't actually load/unload any modules. Regardless, disabling the RedHat ruleset is a worthwhile thing to try in determining what might be wrong. In this case, I don't think he's gotten that far, though.
(grep pop3 /etc/services) netstat -a | grep pop3 | grep LISTEN
If you get nothing, odds are that Xinetd is misconfigured (as available in the online qpopper documentation) or that you have configured and built qpopper in server mode and have not started the service. (man xinetd xinetd.conf)
There is an example file to put into xinetd.d, which was submitted for distribution. I can provide a good, working sample as needed (same one that was submitted for distribution). One need only ask.
Furthermore - If I recall correctly, Redhat does not block connections<->localhost with their firewall setup. So if telnet localhost pop3 does not work, odds are it is not a firewall issue. You may verify this by starting the firewall and reviewing the rules (man iptables)
You recall correctly. RedHat blocks only interfaces from the outside. Blocking anything on the loopback device is a good way to get yourself thoroughly hosed.
