I'm struggling with Exchange Contact Sync. First of all I created an Exchange impersonated user account as per manual. According to this thread I used the "Office 365" button to contact my Exchange 2013. And according to this thread basic authentication needs to be enabled to get rid of the http 401 errors which also worked. (@3cx team - please add this to the manuals) And now: In the IIS logs on des Exchange CAS I see the PBX contacting the server, successful authentication to the /EWS directory and... that's it. Nothing else is happening. Is there any place on the PBX where I can find sync log files so I can trace what the system is doing?