I've got a managed SIP application / server application in Lync 2013, and try to add a header (History-Info and a proprietary one), and I can see it added in the e.Request.AllHeaders collection. But when the request is passed on and i see it in OCSLogger, the header is not there in the SIP-request.
Is there any mechanism in Lync 2013 that will block or remove new headers, or some other reason why this might happen?
It seems the Mediation Server will strip away any headers it does not like. If a call comes in from a SIP trunk on the other hand, it will allow the History-Info header and a few others to be added and manipulated.
And, there does not seem to exist any way of changing this Mediation Server behavior.