I want to know if it is possible to create an exception for some AD Users to receive emails that exceed the Max Message Size defined at Mail Policies - Mail Flow Policy - (my own Mail Flow Policy to limit Max Message Size) in Cisco C300V.
check this - is this works for you?
we are not sure how your polices created so we do not have visibility
here is the document for you to achive :
if this urgent, you can contact you support to help to resolve, remote in to your system and make changes as required.