Display internet name not IP address

I am fairly new to Turnkey and I have one question. 

How do I get apache to stop replacing the Internet name www.mysite.com with the IP address.

I thought I could modify the httpd.conf file, but there is nothing in it, so I asume this is done some place else. Or maybe something I can do in webmin? 

Be cause of various reasons, DNS is external to this server. 

Can someone please point me in the right direction? 

Thank you, 

Mark