if you’re paid user you just need to point your mail.yourdomain.com to business.zoho.com using CNAME record.

Check Here

Could you setup a .htaccess in the sub-domain folder to redirect the sub-domain to the URL.
This should work

RewriteEngine on
RewriteCond %{HTTP_HOST} ^zoho.mydomain.com [NC]
RewriteRule ^(.*)$ https://www.zoho.com/mail/login.html$1 [L,R=301,NC]

I don’t think you can set this up in the DNS Zone.