Reference: FTP Connection Options
These fields specify the name and port of your FTP proxy server. The port field should be included only if the proxy server is listening for FTP traffic at a port other than 21. In general, all connections to an FTP proxy server must operate in ‘active’ mode. The PASV option should NOT be checked.
Note: Beyond FTP operates only with proxies that support native FTP traffic, e.g. a Trusted Information Systems (TIS) FTP Gateway. Beyond FTP does not support CERN based proxies. These servers expect HTTP, not FTP, requests and listen at port 80. Most Internet browsers use HTTP requests to facilitate FTP, therefore “testing” the proxy this way does not necessarily predict Beyond FTP’s operation.