DNS Issues

[Corptech]

I need to segregate 2 networks one for client use and mail hosting and the other for internal use.

On the client network we are using Zimbra Collabaration Appliance for the client emails and on the internal network we are using exchange.

We have 2 separate internet connections but it seems that there was some black magic involved when setting up the Zimbra.

I have tried to change the DNS to split the networks and go through the 2 different Internet connections and all of a sudden the DNS fails in Zimbra and keeps looking at the old email domain.

So in short i was wondering if there is an easy way of changing the internal DNS on the Zimbra box to look at the new mail domains and forget the old domains.

So basically what i want to do is something like the following diagram:

Internet--------203.45.xxx.xxx-----------Zimbra Mail Server

Internet--------120.111.xxx.xxx----------Exchange

But when I point mx record mail.xyz.net.au to 120.111.xxx.xxx the mail server on 203.45.xxx.xxx stops delivering mail because it is trying to find the mail.xyz.net.au and all the clients have now been down for the whole day.

I have since changed the mx record for mail.xyz.net.au back to the 203.45.xxx.xxx in an attempt to get the mail flowing again.

I need help in trying to get this split sorted.

TIA

Allan (Corptech)