This is for network administrators.
In order for users on your network to use Insync, your firewall rules should connect to the following hosts and ports. Otherwise, users may be blocked or denied access from these services.
d2t3ff60b2tol4.cloudfront.net:443/HTTPS for Windows and Mac autoupdaters
For OneDrive, note that these are exhaustive lists and Insync may not be using all the URLs listed there.