iptables -F

# Let input http,ssh, ftp, pop3, smtp
iptables -A INPUT -p TCP --dport 80 -j ACCEPT
iptables -A INPUT -p TCP --dport 22 -j ACCEPT
iptables -A INPUT -p TCP --dport 21 -j ACCEPT
iptables -A INPUT -p TCP --dport 20 -j ACCEPT
iptables -A INPUT -p TCP --dport 110 -j ACCEPT
iptables -A INPUT -p TCP --dport 25 -j ACCEPT

# let output http
iptables -A OUTPUT -p TCP --dport 80 -j ACCEPT

# let dns
iptables -A INPUT -p udp --dport 53 -j ACCEPT

# deny all inputs, allow all outputs
iptables -A INPUT -j DROP
iptables -A OUTPUT -j ACCEPT