Atmail KB: Setting Up SMTP outbound to another port via IPTABLES DNAT
http://atmail.com/kb/2008/setting-up-smtp-outbound-to-another-port-via-iptables-dnat/ if you are on EC2 hosting, redirect all your smpt traffic via SUBMISSION port
http://atmail.com/kb/2008/setting-up-smtp-outbound-to-another-port-via-iptables-dnat/ if you are on EC2 hosting, redirect all your smpt traffic via SUBMISSION port