How to set up DNS service for OS 10.4 server behind a NAT router

[harbortec]

As a neophyte OS 10.4 admin, I have been scouring the net for a "how to" document to set up a simple DNS configuration for an OS 10.4 server running AFP,DNS,MAIL,HTTP behind a NAT router OR using the server as a gateway with two NIC cards, Either config will be satisfactory. An airport extreme will provide DHCP, NAT and port forwarding to the OS 10.4 server for the public services OR act as a simple wireless access point if the config with two NIC cards is used.

The current configuration installed is the AFP,DNS,MAIL,HTTP behind a NAT router (Airport Extreme)

Problem: I have mobile users that connect to the mail server/file server with the following entry server.domain.com in their mail clients, and in their server connect dialogue boxes. They can resolve to the server when connected to the internet from home. We have A and MX records pointing to th IP address of the NAT router by our domain admin. However, the mobile users can't resolve when connected to the office LAN. so the have to type in the local private IP address of the server into their mail clients. How can I fix this? I have used Mac OS X Server Essentials as a guide, but the text doesn't get into specific configurations, rather it tells you about the tools and leaves it up to the Admin to apply them.

Does anyone know how to configure DNS with this set up, or know where I can't find instructions to set up an OS 10.4 SOHO config? Please advise.