webmail subdomain keeping URL

I have a brand new Ubuntu 20.04 with ISPConfig 3.2.4 and apache installed following the automated installation tutorial
Usually I make this to make webmail subdomain:

Code:

Host: webmail
Domain: mydomain.com
Redirect Type: R, L
Redirect Path: https://mydomain.com/webmail/

This change URL address from webmail.mydomain.com to https://mydomain.com/webmail/.
Is there anyway to access webmail but keeping webmail.mydomain.com URL?
I want this because now I'm installing a new mail server for mydomain.com, but web is in another server. So if it redirects to https://mydomain.com/webmail/ it will go to another server, so I think the solution would be to keep URL.
I could make directly site called webmail.mydomain.com but how could redirect this to webmail?
Thanks.

 

I think this is vhost thinggy and normally done copying the relevant vhost template to conf-custom and its install folder, then editing it so that it is update-proof.

If it is just a directive, simply edit it to redirect to the right domain.

 

Finally I create webmail.mydomain.com site and there, in redirect tab, I change this:

Code:

Redirect Type: proxy
Redirect Path: http://server_IP/webmail/
SEO redirect: no

The only problem is that rewrite http to https doesn't work, and if I put https in redirect path I get a cert error (because I don't have cert for IP) and if I change IP for server hostname I have an error.
I will leave it this way.

 

This apache directive works for me:

Code:

DocumentRoot "/var/lib/roundcube"

Thanks

 

This doesn't work for me, public_html doesn't exists under /var/lib/roundcube

 

Roundcube 1.4.3.
Server was installed with the ispconfig autoinstaller

 

Ubuntu 20.04