When Microsoft Silverlight is installed, the DLP clients cannot prevent users from attaching sensitive files to email messages sent through Hotmail.
The compatibility issue between DLP and Silverlight causes this problem. It also involves the way DLP works with HTTP and HTTPS connections.
To address this issue, install DLP 5.5 Hot Fix Build 1326.
Request the hot fix file from Trend Micro Technical Support. For Premium Support Program (PSP) clients, contact your Technical Account Manager (TAM).
Check the Readme file for more information about this hot fix.