When running a support system that can only support members of organisations, some organisations have to be very careful about the recipients of emails - especially in the age of GDPR and data privacy concerns.

After reviewing risks, it's been realised that it would be very easy to accidentally add the wrong person on 'CC' to a ticket.

It would be a great assistance to Agents, if there was some form of trigger mechanism, or app, that could detect when a CC is added whose email's domain name does not match any of the domain names listed against that Organisation.
This should not block a user being added, just flag it somehow to the agent, perhaps through a change in colour of the CC User within the CC field on the ticket view.