Hi, I have been using v6 of 3cx to connect to an exchange 2007 server with unified messaging. Everything is working fine apart from on piece of functionality - Exchange 2007 allows voicemail files normally sent by email to be played via a phone handset. The functionality is called Play on Phone and lets you play your voicemail on your handset or mobile phone etc. When I try to use this function, it silently fails and there is the following error in the server application log: An outbound call to "02890507171" could not be established. The selected outbound IP gateway "192.168.1.112" returned this error: "407 Proxy Authentication Required". The caller ID for this call was "100". For help troubleshooting the SIP response error code that was specified in the event description, contact the vendors who support your IP gateway or IP PBX hardware. You can also run diagnostic tests on your IP gateway or IP PBX hardware to make sure that the devices are operating correctly. Additional information: "A SIP request has failed. The current operation is 'Opening'. The session state is 'Connecting'. The remote participant is 'sip:firstname.lastname@example.org;user=phone'. The response code was '407'. The response text was 'Proxy Authentication Required'." This looks to me like the 3cx pbx is denying access to the exchange server when it tries to contact the handset 100. Anyone else have similar problems and find a resolution?