You wish to connect to an FTPS (FTP over SSL) website using an FTP client via the Symantec Web Gateway FTP proxy.
Resolution
The Symantec Web Gateway FTP proxy does support FTPS, but these are the only available options:
Use Explicit Passive FTPS - requires you opening all high ports on your firewall. Works over both SOCKS and HTTP CONNECT methods and requires one of them to be used.
Use Implicit Passive FTPS - requires you opening port 990 and high ports on your firewall.
Use Implicit Active FTPS - requires you opening ports 990 and 989 on your firewall.
Bypass proxy and go direct to the server picking any of the above 3 options to open ports on your firewall. In this scenario there is also the additional option of Explicit Active FTPS available.