Exchange and network connectivity

Question re: Exchange and network connectivity.
Exchange
Exchange server 2003 SP2 is located physically in a different location in a
colocation facility. It is on a different domain that hosts the company web
presence. DNS forwarders are set to the hosting company DNS servers.
LAN
One internal domain that forwards to an ISP's DNS. Internally PCs have a
host table entry that points to the colocation Exchange server internal IP
(192.168.1.X). It is located on a different subnet address and connected via
VPN.
The problem is that some laptops users cannot connect to email when working
remotely due to the internal IP address entry in Hosts. That's because from
outside there is a public interface. The work around is to have them use the
public IP address. This works, but seems clumsy. Surely, others have
encountered this.

Any ideas? Is there a DNS solution to this?