Please take a look at these screenshots:
next

You can see that "Create Users" check box is checked.
But when new customer send us an email for supporting (E.g new customer email newcustomer@gmail.com (does not exist on our system) send us email support for an issue with existing key M2KAM), the system does not create new user for this customer email.
This case appear when a customer forward his/her ticket to other customer.
Thanks.