How do users, on the internet, connect to the backup server in order to retrieve a file or folder from a file backup? I know how to do it if they are connected to the local area network but can’t find any information to restore a file or folder from a internet connection.
If you forward the ports necessary to connect to the web interface, that is the usual way to do so. Then they can download the files from there, as long as the total download is not over 4GB (any update on the MiniZ situation @Uroni?).
Other than that self-service option, you could always transfer them yourself to a FTP site or other method of file sharing. That would require intervention on your part though.