Using another domain for custom login url.

Using another domain for custom login url.

Hello i have domain example.com ( just for demo ) and have mailbox address like info@example.com. As i found out that i can make custom login url like webmail.example.com to login to my inbox. However for some security reasons, i would like to use another domain say demo.com and my login url be like webmail.demo.com.  Is this possible ??