By default IIS FTP site supports explicit FTPS only. To turn on implicit FTPS, follow these instructions:

  1. Open the IIS Manager. Go to Sites > FTP site, and click Bindings.
  2. Add a binding with the following properties:
    • Type = ftp
    • IP Address = All Unassigned
    • Port = 990
  3. Restart the FTP site and the DefaultAppPool application pool.