digdns.net

Sender Policy Framework - SPF
SPF is an open standard whose goal is to help stop forgery of e-mail domains and some types of spam as well. SPF helps protect the envelope return path.

What is SPF?
A significant majority of spam is forged. SPF allows your mail servers to easily distinguish forgeries from real mail. Importantly, SPF works before the message body is transmitted, saving you the bandwidth cost of downloading the message and the CPU cost of filtering it.

SPF Facts!
SPF is indicated by a TXT DNS record .
SPF is a counterpart of the MX list.

vi /etc/init.d/iptables

#!/bin/bash
#
if [ ! -x /sbin/iptables ]; then
exit 0
fi

start()
{
# clear all
clearall

# Create new chain (I called it filter) which blocks new
# connections, except if coming from inside.
iptables -N filter
iptables -A filter -m state --state ESTABLISHED,RELATED -j ACCEPT
# The next rule depends on what connection to the NET you have
# It could be ppp0 instead of eth0, suit your own needs
iptables -A filter -m state --state NEW -i ! eth0 -j ACCEPT

# Allowed Services - Here you can put all the actually needed