BCC Only emails

Hi guys
I have a request from an internal client, that wants to send notifications emails. He wants to force this mailbox to allow only the BCC field, on each email, and restrict the TO and CC options.
I have Exchange 2013 on a hybrid O365 environment and Outlook 2016 on the internal client.

Is there any way we can do this, with an Exchange rule or any other way ?

To be honest I´m not comfortable with this solution, but I don´t have any other idea. Should this be the best approach ?

Thanks in advanced.
Ricardo Franco