Using FtpEncryptionMode.Auto fails on FileZilla Server

[kenkendk]

FTP Server OS: Windows

FTP Server Type: FileZilla 1.9.4 with Explicit TLS

Client Computer OS: Windows

FluentFTP Version: 50.1.0

Framework: .NET 8

When connecting to the server, using AsyncFtpClient and FtpEncryptionMode.Auto, it fails with the error:

Please call Connect() before trying to read the Capabilities!

Changing to FtpEncryptionMode.Explicit works fine.

Problem seems to be that the FTP server does not allow the initial USER command gives an error 503 that is not recognized by FluentFTP.
Not sure about compatibility with other server, but I would think that issuing the AUTH command as the first command would be the correct way to probe for TLS support.

Server Logs :

When using the Auto setting, this is the server interaction:

FTP Session 77777 X.X.X.X [Response] 220-FileZilla Server 1.9.4
FTP Session 77777 X.X.X.X [Response] 220 Please visit https://filezilla-project.org/
FTP Session 77777 X.X.X.X [Command] USER Username
FTP Session 77777 X.X.X.X [Response] 503 Use AUTH first.
FTP Session 77777 X.X.X.X [Command] QUIT

[FanDjango]

I would think that issuing the AUTH command as the first command would be the correct way to probe for TLS support

Yes, I think you are right.