Can only access OWA using IP but not mail.companyname.com/exchange

Hi,

We are running Microsoft SBS2003.

Currently our users access OWA using an ip address. I would like them to be able to access OWA using the company name instead of the IP address for example https://mail.companyname.com/exchange instead of https://123.123.12.1/exchange.

Does this feature require additional configuration as I have tried mail.companyname and this does not work?

Thanks,

Chris.