settign up a subdomain for roundcube which is not on my webserver

[tachikoma]

Hi,

my mailserver is mail.mydomain.com which goes to mailserver.ip.add.res in my DNS settings and I'd like to access roundcube webmail via webmail.mydomain.com.
My website is configured on mywebserver.ip.add.res which is different from mailserver.ip.add.res.

The standard way to access webmail is webmail.mydomain.com/roundcube. When I enter this, I get redirected to my webservers webmail login.

How do I configure my DNS settings so that I can access roundcubes webmail for example via webmail.mydomain.com on the mailserver.ip.add.res?

I already have entered an A record for webmail.mydomain.com to mailserver.ip.add.res, but I get redirected to the webmail on mywebserver.ip.add.res.
Do I have to wait for the DNS chache to clear, or is there anything else I have to configure?

[SKaero]

You can't do the setup you want with DNS alone the server that Roundcube is hosted on would also have o be configured to load Roundcube when you went to your webmail.example.com domain.