activate subdomain link to webmail on a multisite cpanel account

well, this is the scenario.

Cpanel accounts creates some redirection to have a nice webmail.mydomain.com (also accessible via mydomain.com/webmail)

When multisite activated, the use of subdomain webmail does not work, for any domain parked on the multisite install.

Is there a way to restablish that ?

Because it is muc more nice than the /webmail/ for clients....

any tip ?