It sounds like your users can't resolve the DNS name. If your users are on the public Internet, then you need to have a domain name registered within the Internet's DNS infrastructure. Most companies accomplish this by calling their Internet Service Provider (ISP) and asking the ISP to add the domain name and associate it with a specific IP address. It's also possible to host the DNS services internally but the best place to start is by calling your ISP.
This was first published in May 2001