Last night I try to figure out why I can’t use my subdomain to cpanel and webmail. After a few minutes, I surrender. Then I asked my hosting provider why I got that problem. And here what they replied:
You cannot simply create a subdomain to enter to your cpanel and webmail.
You will need to install a proxy in the subdomain in order to access to the cpanel and webmail .
We can install it for you but we need you username and password for your cpanel.
Please give us your cpanel login details and we will install it for you asap.
I asked them again, can I make it by my own and they gave me a link where you can use the script to create subdomain for your webmail and cpanel.
Here is the link: http://www.cpanelproxy.net/autoinstall
So, if you have problem like mine, you can try this script.