Use the TLSPORT statement to set the secure port on which the FTP client or the FTP server implicitly protects the FTP session with TLS.
If you want to use port 990 for unsecured FTP sessions, use this statement to select a different secure port for implicit secure FTP sessions. If you want to disable support for implicit secure FTP, use a value of 0.
Result: The specification of a TLSPORT does not cause the server to listen on that port, it only specifies that when the port is used it will behave as an implicit TLS port. See FTP server cataloged procedure (FTPD) parameters for information about how to specify the port for the listener.
TLSPORT 0