I have iptables ruiing in our internet gateway which is a redhat linux 9 box. The gateway uses two NICs, one with public IP and the other with private IP. I also have squid running on it.
The problem is using squid, I am able to block unwanted sites (Like adult sites) by the url string matches.(Although I would love a better way). But as it was not possible for the LAN users to use mail clients like Outlook etc, through squid, I decided to use iptables with masquerading and let them access internet through it.
How can I block unwanted sites (Ex: adult websites) using iptables, or if possible, how can I use mail clients etc., like outlook etc, using squid.