assignment of tasks to customers not yet registered and management of the CC field

[Fabio Martignago]

Hello, please follow my idea:

From: Sender email
To: Project email
CC: email to the Assignees  (one or more)
Object: Task to be completed

If the assignee exists then ok, he will find the activity on the customer portal.

If the assignee does not exist a portal registration notification arrives to the assignee and then he will find the activity on the customer portal.

The assignee can be an existing agent or a customer

So the questions are: how can I handle the CC field and How can I teach the system to manage the unknown/new customers?