Reference: Advanced FTP Server Options
This option applies only to secure FTP connections. It is used to provide what some call “firewall friendly” ftp. It causes the ftp client interface to make a secure SSL/TLS connection with the specified server for the purposes of exchanging login information. Once the session is established, it sends a CCC command that reverts the session to clear text. Only file data is still encrypted between the client and the server. All commands related to transferring files are transmitted clear text. This allows firewalls that perform packet filtering to recognize and properly handle the FTP connections.
Note: This is applicable only to standard FTP traffic. Beyond FTP connections do not require that security be relaxed. All traffic on a Beyond FTP connection is encrypted at least once and may be double encrypted if the private key security is engaged.