We stopped using Notes mail several years back and my (leftover) 8.5.3 mail db doesn't have rules in the tools dropdown.

Can you create a rule that forwards to a DbLookup value since the 'cc' is to be the sender's manager?

Can that cc be an appended list since you don't want to wipe out user entered cc names?

Is this something that can be deployed universally and not removed by the end user?

I was thinking that the mail template would need to be modified to use the cc field's Input Translation formula to append a DbLookup of the manager's name to the existing cc list. In this way, the end user can't overwrite the values and they can't bypass the code or remove the rule.