Well, unfortunately to forward mail you have to have something to receive it in the first place, which means you have to have an MTA (Mail Transfer Agent) package installed. And if you can get an MTA running then all you really need to have a useful mail server is an IMAP or POP server running. So my recommendation to you is to visit
www.postfix.org and check out the documentation. Postfix is a very powerful MTA, and is quite easy to configure. Then check out Courier-IMAP when you are ready for that.