Iptables Rules for IPv4 and IPv6

Not sure what you mean by "hardened" version of rules here. A correctly configured firewall only allows through that which is explicitly allowed, which is hardening over allowing everything. This is essentially what the article in question does, you just add rules to allow through the traffic you want and remove what you don't want. The next level of network wise hardening after that is separating the firewall physically from the box, and doing deep packet inspection. That is probably an overkill for everyday mail and web servers.

Hi emestee,

Thank you for your response and for the clarification.

Cheers.