In this paper, we present a privacy control mechanism called PDE (Privacy Data Envelope) allowing users to protect their privacy sensitive content travelling over social and communication networks. Our solution is based on privacy policies expressed by the user and associated with his content. This approach makes use of a decentralized architecture carried out through a PDE feature that has to be added to the existing application access tools like email clients and web browsers. A prototype has been developed to embody the PDE paradigm and to illustrate a scenario where such envelopes cross the boundaries of enterprise social networks and other communications tools. Preliminary performance evaluations were done helping the understanding of the PDE plug-in behaviors and computation overhead.