Firewall auf dem gateway:
iptables -A INPUT -p tcp --dport 8006 -j ACCEPT
iptables -A INPUT -p tcp --dport 25 -j ACCEPT
iptables -A INPUT -p tcp --sport 25 -j ACCEPT
iptables -A INPUT -s 185.97.4.0/22 -j ACCEPT
iptables -A INPUT -s 62.141.35.6 -j ACCEPT
iptables -A INPUT -s 127.0.0.1 -j ACCEPT
iptables -A INPUT -s 8.8.8.8 -j ACCEPT
iptables -P INPUT DROP
 
   

Firewall auf dem mailbackend:
 
iptables -A INPUT -s 185.97.4.0/22 -j ACCEPT
iptables -A INPUT -d 185.97.4.0/22 -j ACCEPT
iptables -A INPUT -s 62.141.35.6 -j ACCEPT
iptables -A INPUT -s 127.0.0.1 -j ACCEPT
iptables -A INPUT -s 8.8.8.8 -j ACCEPT
iptables -A INPUT -p tcp --dport 587 -j ACCEPT
iptables -A INPUT -p tcp --dport 110 -j ACCEPT
iptables -A INPUT -p tcp --dport 143 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j ACCEPT
iptables -A INPUT -p tcp --dport 25 -j ACCEPT
iptables -A INPUT -p tcp --sport 25 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j ACCEPT
iptables -A INPUT -p tcp --dport 4190 -j ACCEPT
iptables -A INPUT -p tcp --dport 993 -j ACCEPT
iptables -A INPUT -p tcp --dport 995 -j ACCEPT
iptables -P INPUT DROP