This article applies to the following:
6.x Briefcase for Windows, Email Manager for Outlook, Contributor Pro
Engage communicates with the SharePoint though web services, the details of which are available on msdn here.These web services calls are transmitted over HTTP (or HTTPS) using TCP.
Engage also uses FrontPage RPC methods to communicate with the SharePoint server. FrontPage RPCs are also transmitted over HTTP(S) and TCP. Details of the FrontPage RPC protocols can be found on msdn here.
The services described above are installed and enabled on SharePoint by default. Because they are layered on top of TCP/HTTP, communication works over most WAN/VPN and/or wireless connections, as well as a standard LAN.
Colligo’s Windows Products (Briefcase for Windows and Email Manager for Outlook) also use SharePoint’s Client Object Model to communicate with the SharePoint server: the details of which are available on msdn here.