The MOST effective technical approach to mitigate the risk of confidential information being disclosed in email attachments is to implement:

ISACA CISM Exam syllabus in brief:

Information Security Governance    
A. Enterprise Governance
B. Information Security Strategy

Information Security Risk Management    
A. Information Security Risk Assessment
B. Information Security Risk Response

Information Security Program    
A. Information Security Program Development
B. Information Security Program Management

Incident Management    
A. Incident Management Readiness
B. Incident Management Operations