secure fxp problem

[Harm]

If the 2 other servers are enforcing a secure fxp policy, you won't be able to fxp from/to them without enabling ssl/tls site to site transfers. If the 3rd site doesn't require secure fxp, maybe it allows it anyway. Try to enable secure site to site transfers for the 3rd site.

You said other ftp client(s) may allow to bypass the server's security policy. That's surprising. If it's true, it's more likely to be a flaw on the server side than a "feature" of the ftp client. Could you provide more details about this?