Originally Posted by n!x
(2) The next thing is confusing. Let's say i'm hosting this domain on my Ubuntu box www.123.com
and my mailaddress should look something firstname.lastname@example.org
What should the "server1.example.com" look like in my case?
This has nothing to do with the domains you want to host on your server. You can still use server1.example.com or server1.123.com or h6535.anyotherdomain.com.