Ok Basically the way it works is that when you register a name on the internet, that name will be connected to a nameserver or a dns server for examle
http://www.domain.com is set to goto 10.0.0.1 where 10.0.0.1 is a nameserver or dns server, then this name or dns server will be setup to forward either http traffic for a web server or mail MX traffic for a mail server as an example an entry in the dns server will say "www.domain.com MX 10 10.0.0.50" where 10.0.0.50 is your static IP that your server runs under..When someone sends mail to user@yourdomain.com then first incoming mail server will check to see where youdomain.com is then the dns server will tell it goto your IP address 10.0.0.50 for mail delivery as specified on top...When mail comes to your box, sendmail running on you server will listen on port 25 for any incoming mail and decide either to accept or reject...If user has an account then it accepts it otherwise it will reject it.
So here is what you need before doing anything with mail server software on you box.
Need a fixed static IP
You need to link youdomain.com to a free dns server as stated above in one of my messages
An entry in that free dns server to point back to your IP address.
If you do all that, you would at least start recieving and sending mail with out any extral configuration. To use outlook to connect to your server then you need to install a pop server on you machine. Some Linux distro will have it included if not download qpopper and install it.
If you have anyother questions please post one at a time or step at a time and I will help you in more detail.