Sub-Domain redirect

Hi,

I'm moving a load of cPanel accounts over to a new server with VirtualMin Pro on which is going fine but one thing has stumped me.

I get and understand the subserver, alias etc but I want to setup a redirect so that mail.domain.com forwards directly to domain.com/squirrelmail

What's the best way? Should I create a new sub-server and setup a root redirect to that URL or not install squirrelmail on the main domain and just setup a subserver mail.domain.com that has squirrelmail installed on it?

Cheers in advance, Ian