Yes, but this concerns only configuration information of your SYNCING.NET user account and your SyncNetworks. Your Outlook data and files are always stored locally on your computers. The data transfer between your computers is naturally cryptographically secured.

Update: Only if you are using the “Store-and-Forward” feature (since Version 2.0.3082; accessible under SYNCING.NET “Configuration -> Options -> General Settings”), the cryptographically secured change requests from the last computer online in your SyncNetwork will be stored on our server until another computer comes online and downloads the change requests automatically. Please note that only 200 MByte of change requests (at a maximum of 20 MByte per file) can be stored. After each peer has downloaded the change requests, they will be deleted immediately from the server. With this feature it is now possible to sync computers which are never online together at the same time.