Hi Martin, many thanks for your help, adding SessionOptions.AddRawSettings "FtpHost", "0" to my VBS script did the trick, brilliant! I could not get the GUI to play, but the .NET works and that's all I need.

My apologies, FEAT for WinSCP was just a red-herring.

Thanks again,

That's probably just a side-effect. SmartFTP needs to find out that the server supports the HOST command. For that it runs FEAT command. By default it runs it only after authentication, what is too late.

While in WinSCP, you can explicitly configure it to use the HOST command, even without using FEAT command. Did you tried that?

Attached is an SmartFTP log (I have only changed the server name). They are sending the FEAT before the HOST command presumably they chose FEAT because it can be run un-authenticated.

I do not know why this enables me to connect to the particular server that I need to, but it does and I cannot connect using WinSCP.

To support virtual FTP hosts, the client has to send HOST command, not FEAT command.
WinSCP does support HOST command:
https://winscp.net/eng/docs/ui_login_ftp

I am guessing but it looks like SmartFTP's "fix" for virtual FTP hosts. "to differentiate between multiple DNS names that are registered for a single IP address."

SmartFTP https://www.smartftp.com/en-us/support/kb/2638

FTP Spec https://datatracker.ietf.org/doc/html/rfc7151

Sorry, but I do not think this requirement is anyhow backed by an FTP specification.

In SmartFTP for FTPS-Explicit there is a Connection option called "Send FEAT" with a value of "Send before and after login". The effect is to send a FEAT command immediately after connecting before the AUTH, USER etc. and again another "normal" FEAT after the login.

The FTPS server I have to access needs this double FEAT business otherwise it returns the error "534 Local policy on server does not allow TLS secure connections.".

I would like to have this in WinSCP.net as my software is all based on the WinSCP .NET & COM and not SmartFTP.

Could you add a SessionOption to specify when you send the FEAT command, e.g. "After Login" or "Before and after login"?