Is it possible to post mail with the webmail.domain.com subdomain? is it possible to provide this as a standard with an automatic webmail dns record in each customer domain?
Yes this should do → 2 - SSL For PostFix/Dovecot - CyberPanel
And more detailed guide is available here → Achieve 10/10 Email score with CyberPanel! - CyberPanel
example : http://webmail.pratikonmuhasebe.com/ customer email login page
so we can’t do like that.
You can do that How to remove port 8090 from CyberPanel - CyberPanel