Using Outlook

I have a small Novell network and use a mandrake 8.2 Linux box for a proxy server. I use this strictly for Internet. There is no other services (DNS, Samba, etc) in use on this machine. Our email is hosted on a non company web server and I need to get Outlook to work on the users windows machines, mostly win2k. the only other thing running on the Linux box is GuardDog firewall. Guarddog shows a mail icon which I have activated but I still can’t get emails to the windows machines. Does anybody have any quick and easy recommendations to resolve this.