redirect smtp on one IP to another IP

I'm attempting to re-reoute smtp traffic that will come to my web server address to our new mail server. Both are Centos / Interworx systems. It does not seem to be working.

I've modified the /etc/afp/preroute.rules as follows:


eout "{glob} loading preroute.rules"

# place your custom routing rules below
iptables -t nat -A PREROUTING -p tcp -d [mywebserverip] --dport 25 -j DNAT --to-destination [myemailserverip]

any help would be appreciated.