Email auto register

[blackmask]

Hi,
In ispconfing if we want to add email user, just create the email in ISP Manager->Domain Site->User&Email
in this form it will ask :
Real name, Email Address User Name...etc + Advance Setting + Spamfilter

My situation is:

I want to give a free email to my user and i want them to register their email by themself. Like yahoo and gmail.

I try to find the above form code but still didn not successful. Does some body know what the above form do.. for example the Real Name, Email Address wheere is place... which table.. and etc...

Can somebody quide me..

Thanks..