ispconfig2 spam security

[tomt2002]

i wan´t to use a iptables comfiguration to make sure that only valid users could send emails and not a spammer software like "darkmailer".

which users must be allowed to send emails if i would use a configuration like:
iptables -A OUTPUT -d 127.0.0.1 -p tcp -m tcp --dport 25 -j ACCEPT
iptables -A OUTPUT -p tcp -m tcp --dport 25 -m owner --gid-owner mail -j ACCEPT
iptables -A OUTPUT -p tcp -m tcp --dport 25 -m owner --gid-owner mailman -j ACCEPT
iptables -A OUTPUT -p tcp -m tcp --dport 25 -m owner --uid-owner root -j ACCEPT
iptables -A OUTPUT -p tcp -m tcp --dport 25 -j REJECT --reject-with-icmp-port-unreachable

thanks for any information and your help !

best regards
tomt2002