Before performing this task, you must have a Web publishing rule that uses forms-based authentication for Outlook Web Access.
To block attachments from reaching Outlook Web Access clients
In the Forefront TMG Management console, in the tree, click the Firewall Policy node.
In the details pane, select the applicable Web publishing rule that uses HTML forms-based authentication for Outlook Web Access.
On the Tasks tab, click Edit Selected Rule.
On the Application Settings tab, in the Exchange Publishing Attachment Blocking section, select Public computers or Private computers (or select both options), and then click OK.
In the details pane, click the Apply button to save and update the configuration, and then click OK.
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