Attachment Defense has two components:
Attachment Defense Reputation Service
Protects SMEs from known attachment-based threats by checking their reputation before delivery. Attachment Defense Reputation is available in the Proofpoint Essentials Business, Advanced and Professional packages.
Attachment Defense Sandboxing
Protects SMEs from zero-day attachment-based threats by sandboxing suspicious attachments before delivery. Attachment Sandboxing is available in the Proofpoint Essentials Advanced and Professional packages.
For more info, see attached Data Sheet