Explicit: If a client does not request security, the FTPS server can either allow the client to continue insecure or refuse/limit the connection.
Implicit: A client is immediately expected to challenge the FTPS server with a TLS/SSL ClientHello message. If such a message is not received by the FTPS server, the server should drop the connection.
So If I own only the client side, then what can I do to allow an FTPES connection to only use a secure connection? Under a non-windows OS.
IPtables/pf rule? Proxy? or What can I do?