port forwarding???

I have install zimbra and have a DNS on Windows server 2003

I have set the record in DNS to acces zimbra web mail

with mail.example.com to read mail

and mail.example.com:7071 for admin

Is it possible to "create a virtual url" like admin.example.com wich will forward to mail.exaple.com:7071

url will be used only in intranet

where to do it ? more generally if I have any web server on dedicated port where should I to do it?

on server side or dns or ????

thanks