Develop outlook API to work search keywords and tag such emails including attachments in all folders as PII or Not PII. If keywords are not available then also user can tag them into PII or non PII categories. Even if auto PiI is tagged, final say will be on user. If PiI is tagged then emails will be deleted based on purpose is closed. User can set the rules tagging PiI email to close. Close status emails will be deleted automatically after a pre- defined period. All PII where status is not closed will ask user to review and mark them as status closed or open. Report of non addressed email with ageing can also end generate.
Any email tagged as PII will also be asking recipient within the same domain to install API to ensure all features of API applies to recipient system as well.