Mail Routing using SendMail

My linux technician has left my company and I have this linux server but not much knowledge on configuring it. I primarily use it to route mail. I set the MX record on the DNS to point to this server for Domains I host and then have it route all their mail for a particular domain to an external email box on other servers. I need some step by step procedure to do this. Talking to my tech, he says not to use linuxconfig because it doesn’t change things correctly. He says I need to modify the files manually. Can anyone tell me why linuxconfig won’t work or how to do this manually, step by step? Can linuxconfig be run remotely? When I try using telnet on WIN95, the menus get jumbled and I can’t see what to pick.