Webmin, iRedMail, and other hosts

suber

Hi,

I have a VPS with ubuntu 20.04 running on it.
I have also been given a webmin panel (installed in this ubuntu) to administer my os, by my vps provider.
I want to install a mail server on this vps, and I want to register it in my domain: mail.my-domain.com.
The problem is, whener I change my vps hostname to mail.my-domain.com and install iRedMail, pointing to it,
my webmin panel which resides in my-old-hostname.com:10000, doesn't show anymore in the old-hostname.com.
I know that a server can only have one hostname, so how can access my webmin server while installing iRedMail to the new hostname?