Hi,
one CT works as a mailserver, reachable via NAT from external network with the following iptables-roules:
IP="xxx.xxx.xxx.xxx"
echo 1 > /proc/sys/net/ipv4/ip_forward
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
iptables -t nat -A PREROUTING -p tcp -d $IP --dport 25 -i eth0 -j DNAT...