I am sorry for a somewhat misleading previous reply.
Unfortunately, the address book backup is not provided for the RU Server yet, but we plan to implement this feature in our future updates.
You can restore the Server address book from the Viewer's address book or its backup. The Viewer's address book backups are located in the C:\Users\YOUR_USERNAME\AppData\Roaming\Remote Utilities Files folder. Please note, note that the AppData folder may be hidden. You will need to enable "Show hidden files and folders" in your system first.
To restore the address book on the server's side, please set up a sync server role by following this guide
. Then you can just drag the connections and folders to the new synced address book in the Viewer.
Please note, that the connection in the address book does not affect the Host being online or offline - it only depends on the Host being online/offline and if it's available to connect to. Also, please note that the address book synchronization does not affect the ability to connect to the Host. For more information on the connection statuses, please refer to this Documentation article
Hope that helps.