When using the Skype for Business web application, DLP is not running detection on file attachments.
The default Skype application is enabled already in Global Application Monitoring.
Data Loss Prevention 15.5
Data Loss Prevention 15.7
Skype for Business uses a different exe than the desktop Skype application.
1. In the Enforce Console, navigate to System > Agent > Global Application Monitoring.
2. Select 'Add Application' and set the following:
3. save your changes.