Please excuse my utter ignorance to this area of networking, but this is just something ive never really come across until my recent experiences with linux.
I also realise this should probably be in the newbie forum, but i would rather get fully qualified explanations than those aimed at the village idiot. (no offense to those in the newbie forum)

First of all i would like to say that after only 2 weeks of having my own linux machine, i really am impressed. Ive taken to it well after having used windows and windows only for all my computing life.

The background:
I still primarily use my windows xp box, but in an effort to learn more about the industry in which i work i have set myself up a copy of debian on my old machine. it is currently sat out in the corridor with no keyboard mouse or monitor, and therefore gets used entirely via ssh session with putty.

My aim is to experience the most i can from this machine before i ever venture so far as to set it up as a useable desktop computer. I have battled with setting up proftpd, apache, samba (still struggling here), and several other apps, but the one that still has me baffled is exim.

I would like to set up my own mail server, and allow the other chaps in my house to send mail internally and if possible, externally.

The problem is this. I see from my trawling through exims config file that there are many references to the "domain". Now i have no idea what is meant by this.

This mail server will not be receiving any mail from external mail servers, and therefore, shouldnt need a domain name. Besides that it does not have a public IP address, and i have no means of setting up NAT to allow it to be addressed directly from the internet.

From my initial read of the config, i have made the deduction that this "domain" is simply a name of sorts for the internal network, and bears no real importance once mail is sent off in to the big wide world. But i cannot be sure of this, so would someone please enlighten me as to what one of these magical "domains" is, and possibly give me some tips for acheiving my goal in exim?

As i said. Please excuse my ignorance and utter newbieness. I can imagine this is like a windows user asking me how to start notepad.

anyone?