MTA on 2 ports?

[brained]

On my qmail based gentoo server it listens on port 25 and (for my customers using wifi hotspots) on port 2225 using this method:

http://forums.gentoo.org/viewtopic-t-119412-highlight-qmail.html

How would I accomplish the same with Zimbra and Postfix?

[marcmac]

iptables -t nat -A PREROUTING -d -p tcp --dport 2225 -j REDIRECT --to-ports 25