So I've read http://www.virtualmin.com/documentation/id,webmail_and_virtualmin/ but it's not clear to me quite what you mean.
In my setup I have hub.tld which is just a holding domain for webmin. Under that I have virtualmin domains website1.tld, website2.tld. So I could run the roundcube install script for both. I think this would end up with website1.tld/roundcube and website2.tld/roundcube which I could then alias to say webmail.websiteX.tld. Or, according to the docs, the recommended way is just install roundcube once then redirect to that one. But if I understand this correctly then, assuming I install on website1, webmail.website2.tld would change in the URL to website1 which is not what I'd want to happen.
Do I have that correct? Is there any way to have one install of roundcube but have webmail.website1.tld and webmail.website2.tld as access URLs that don't change?