I am trying to transparently filter outbound SPAM from one of my hosting boxes. I have set up an external mail server that filters SPAM and now I am looking for a way to route all outbound SMTP traffic from the hosting server to the Mail Scanner with IPTables.
Eg. -- Outbound SMTP (22.214.171.124 port 25) --> MailScanner (126.96.36.199 port 2500)
So far my closest attempt has lead me to LAND attacks showing on our CISCO firewalls.
iptables -t nat -A POSTROUTING -o eth0 -p tcp -j SNAT --dport 2500 --to-source 188.8.131.52