2.2.3.3 Protected Voice Message Property

The PidNameXRequireProtectedPlayOnPhone property (section 2.2.5.14) is set on the outer message of the protected voice message. When this property is set to "TRUE", the client that renders this message MUST NOT allow users to listen to the voice attachment by means of the e-mail client. The client MUST offer the Play-On-Phone feature to the user as the only option for listening to the voice message.