Automatically create staff-account for new staff when they e-mail

Case: I have a few teams using Zendesk, and loads of colleguea's who don't usually use Zendesk. However, loads colleguea's are CC'd in mails sent to Zendesk, and reply on them. 

If this happens, Zendesk automatically creates an account for them, and gives them an end-user-role. Therefore their comments are registered as public comments. 

I would love for Zendesk to automatically give them the role of 'staff', so their comments are internal. Zendesk could easily distinguish them on the use of the domain in their e-mailadresses. Just a configuration field in the admin center where I can put the several domains of our company to let Zendesk know they are staff, not end-users. 

This releases us of the manual process of creating user accounts for people who probably never need it, and prevents customers to get updates which should not be sent.