Symantec Messaging Gateway can scan email attachments with the following extensions for spam:
To scan text-based attachments
In the Control Center, click Spam > Settings > Scan Settings.
On the Email tab, under Text-based Attachment Scanning, click Scan text-based attachments.
By default, this option is enabled for a new installation and disabled for upgrade. Enabling this option may result in slower performance of Symantec Messaging Gateway. When this option is disabled, Symantec Messaging Gateway does not use all scanning technologies for evaluating the attachments for spam.