hi i have a new installation of v15 PRO with all the updates what i need to do as title says is to sync contacts from on-premise Exchange 2016 with 3CX the company has one user account (firstname.lastname@example.org) in Exchange that holds almost 5000 contacts. i need to sync this contacts with 3CX so that all the extensions can see who's calling from the outside if the number is present in Exchange. Phones are Snom D375 so this shouldn't be a problem with the snom_phonebook.xml file the problem i have is the connection between Exc an 3CX. the configuration was done according to the blog for this integration. Exchange impersonated user is created. settings in 3CX are there i see this error in the log files 2016/11/17 15:26:20.283|2780|0031|Info|Synchronization of GAL started... 2016/11/17 15:26:20.283|2780|0031|Info|Synchronization of public folders started... 2016/11/17 15:26:20.306|2780|0031|Warn|Microsoft.Exchange.WebServices.Data.ServiceRequestException: The request failed. The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel. ---> System.Net.WebException: The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel. ---> System.Security.Authentication.AuthenticationException: The remote certificate is invalid according to the validation procedure. what certificate? where to get it and what to do with it? has anyone done this before and knows what additional steps must be do to get this working?