Outbound emails restriction within internal domain

Hello, I have I administrate a shared hosting server and i want to make a restriction just for two email accounts within one of cpanel users. So i have domain @example.com and i want to restrict just acc1@example.com and acc2@example.com to send emails only within their domain. If i make changes at exim system filter file, does this effects other email accounts within this domain ? Or is that any risk that this change impact other domains which are hosted in the same server ? Could anyone help me whith the exact syntact of the condition i need to put in exim system filter file for this case ? Thank you in advance