The attached malicious file is not stripped from e-mail in the following scenario:
Traditional Anti-Virus is configured in Proactive Mode (in SmartDashboard, go to "Threat Prevention" tab - in the left pane, open "Traditional Anti-Virus" - open "Security Gateway" - open "Mail Protocols" - click on "SMTP" - check the box "Activate Proactive Detection" - install policy)
The name of malicious file (that is attached to e-mail) contains non-ASCII characters (e.g., Japanese, Chinese, Korean)
Cause
Traditional Anti-Virus in a Proactive Mode does not support file names that contain non-ASCII characters (e.g., Japanese, Chinese, Korean).