SMTP on a Secondary IP

From Whitey's Wiki

smtp on secondary ip

The easiest way to make this happen is with an IPtables rule, and this rule will work across all MTAs.

root# iptables -t nat -A POSTROUTING -o eth0 -p tcp -j SNAT --dport 25 --to-source <new IP>

The above rule will re-route all traffic to your alternate IP address, before it is presented to your MTA.