3.2 Ms-Sensitivity Details
The Ms-Sensitivity header, as specified in [MS-SIPRE], SHOULD be used in Dial Out (Play-On-Phone), scenarios when the user requests a voice mail message to be played on the phone from an application. In such a scenario, the unified messaging server sends an INVITE to the user and uses this header to indicate to the protocol server that the call MUST NOT be rerouted back to voice mail and call forwarding when the Play-On-Phone call is not answered by the user. In this case, unanswered call forwarding or immediate call forwarding MUST NOT be applied. The unified messaging server sends such an INVITE through the Exchange Web Service (EWS), as specified in [MS-OXWUMS]. The trigger point for this is an event sent by EWS.<1>
The unified messaging server supported by this protocol uses the Ms-Sensitivity header with the private-no-diversion parameter, as specified in section 2.2.2.
Use of other parameters, as specified in [MS-SIPRE], is out of the scope of this extension.
Note that in Play-On-Phone INVITEs that originate from the unified messaging server, the URIs in the From header and the To header MUST point to same address. This is because the protocol clients have special logic that checks for this condition and allows the protocol client to ring for Play-On-Phone calls, even if the user has manually set himself or herself to the "Appear Offline" presence state.
Unified Messaging Server Behavior
A unified messaging server SHOULD send a Ms-Sensitivity header with the private-no-diversion parameter in Dial Out or Play-On-Phone scenarios.
Protocol Server Behavior
If a SIP INVITE contains a Ms-Sensitivity header with the private-no-diversion parameter, unanswered call forwarding or immediate call forwarding MUST NOT be applied.