AIP question on alerts

AIP can auto classify based on sensitive information types such as PCI which will apply access permissions to the document. Users not allowed access could not get access, even if emailed the document, unless you use AIP P2 which has ability for business users to provide permission overrides with a business justification. Then you would want to explore the Azure and Office 365 audit logs for capturing and alerting on the override.

If you are trying to audit and train business users who email an AIP document to an unauthorized user, despite the recipient being not able to access the document, I would explore Exchange transport rules to see if you can apply an alert looking for the AIP classification on the document.