Welcome! This forum has a treasure trove of great info – Scouters helping Scouters! Just a heads up, though - all content, information, and opinions shared on this forum are those of the author, not the BSA.
It is impossible to force a Scout, or anyone else, to copy another adult when sending an e-mail from a standard e-mail client.
Best practice today is the adult recipient of a one-on-one e-mail or text from a Scout should immediately reply to the Scout with the parents or another leader on copy, reminding the Scout to always copy a 2nd adult on all communcations.