I see that this is in the "will not implement" but maybe this will help
I think this would tie in to having different departments in ITFlow (Sales, Billing, Support, Etc) and then having mailboxes for each of those departments. Internal Users (Technicians) can be then mapped to the different departments as needed.
The folks on the Sales team don't really need access to the tickets that the Technical team put in, etc.
I hope that clarifies it. If not, I am open to providing information from other systems that may help