Adding subdomains for email to use a Custom URL

Adding subdomains for email to use a Custom URL

Hi,

I have added my domain (www.example.com) and changed the MX records on the domain.
The e-mail abc@example.com sending/receiving works perfectly. I am on the free plan to try out the service.

I need for the e-mail to be accessible via a subdomain:
email.example.com
so I added a CNAME to the DNS records of my registrar. Now I can hit it (email.example.com) and get the e-mail login zoho page fine, however after logging, in the URL changes back to mail.zoho.com/..... in the mail box.

Is there anything left? According to this:
https://help.zoho.com/portal/en/community/topic/custom-url-for-zoho-mail-portal
I need to add the subdomain to Zoho as well, but cannot find any way to do it. Is this available for the free plan?
If so how?

Amit