Hello, Emanuele
If they're simply submitting a ticket for a different email address that's part of your original domain -- for example, parts@your_domain.com versus support@your_domain.com -- then you want to create a new department and group(s) and then add those email credentials for that department. You don't need a different Brand.
Brands are used for something like a different company you were supporting.
Derek Curtis
COO
SmarterTools Inc.
www.smartertools.com