Yes I have had the same question, so this is answered mine for 50% I guess.
I have some sites I want to move from my old ISPC2 to the new ISPC3 and yes I know they are 2 different systems so I CAN'T migrate.
I have set up my main site according to this image:
With the help from this
howto. I know its not exactly the same but the howto was intended for ISPC2 so I used the dns wizard and made some things up.
I want to start fresh this time, and look more like a real ISP....
so with separated pop3, smpt and web-mail.
(in ISPC2 I just used for all www.mydomaim.nl
I think that if I set up a new site I must use the name servers as in the image, so the site will be reachable.
If I want the user of that site to reach his mail can I just tell him to use the pop3 and the smtp as in the image with his own user name and password? For reaching his mail?
If yes what is the purpose of the dns zone? Is this just for site's that uses different ip addresses? So if I set up (for example) a web-shop that uses SSL for its paying method, I have to use a second ip and than I have to create a second dns zone.