I inherited a Linux based Firewall and I have been learning a bit about iptables. I seem to have a machine spamming which is causing Blacklist issues. I tried to add some lines to only allow mail from trusted sources; mainly the Exchange cluster servers and the Owa server. When uncomment out the REJECT line, I can send mail OK but no messages are received from external sources. Below is the code, please pick it apart and tell me where I'm wrong and what I haven't picked up yet Thanks in advance for your cruel honesty...
# FORWARD
# Rule 1 to allow outbound mail only from Exchange server
# Rule 2 to deny any other outbound port 25 traffic
iptables -A FORWARD -p tcp -s 172.16.x.xx --dport 25 -j ACCEPT
iptables -A FORWARD -p tcp -s 172.16.x.xx --dport 25 -j ACCEPT
iptables -A FORWARD -p tcp -s 172.16.x.xx --dport 25 -j ACCEPT
iptables -A FORWARD -p tcp -s 172.16.x.xx --dport 25 -j ACCEPT
iptables -A FORWARD -p tcp -s 172.16.x.xx --dport 25 -j ACCEPT
iptables -A FORWARD -p tcp --dport 25 -j LOG --log-prefix "REJECTING SMTP CONNE$
iptables -A FORWARD -p tcp -s 172.16.x.xx --dport 25 -j REJECT
#iptables -A FORWARD -p tcp --dport 25 -j REJECT
# OUTPUT
# FORWARD
# Rule 1 to allow outbound mail only from Exchange server
# Rule 2 to deny any other outbound port 25 traffic
iptables -A FORWARD -p tcp -s 172.16.x.xx --dport 25 -j ACCEPT
iptables -A FORWARD -p tcp -s 172.16.x.xx --dport 25 -j ACCEPT
iptables -A FORWARD -p tcp -s 172.16.x.xx --dport 25 -j ACCEPT
iptables -A FORWARD -p tcp -s 172.16.x.xx --dport 25 -j ACCEPT
iptables -A FORWARD -p tcp -s 172.16.x.xx --dport 25 -j ACCEPT
iptables -A FORWARD -p tcp --dport 25 -j LOG --log-prefix "REJECTING SMTP CONNE$
iptables -A FORWARD -p tcp -s 172.16.x.xx --dport 25 -j REJECT
#iptables -A FORWARD -p tcp --dport 25 -j REJECT
# OUTPUT