I have installed zimbra 5.09 in Ubuntu 8.04 LTS.

My servers are behind the router I have set split DNS and I am able to send and receive mails. My problem is

I have mydomain.com and mail.mydomain.com

I have redirected my 80 port from the router to my zimbra its working fine.
I need a help in setting up like this

I have sub domain say mail.mydomain.com when ever I type mail.mydomain.com in my browser it comes to my router then to my zimbra thats fine.

I have domain say mydomain.com when ever I type mydomain.com the router redirects to my zimbra. but what I need is my mydomain has to be served by another web server. How can I achieve this.