The following FTP commands are the only ones supported by the FTP Proxy in BorderManager 3.5 & 3.6. (I am not yet sure about 3.0, but assume it is the same).
user
pass
type
cwd
mdtm
pasv
port
list
rest
retr
size
Other FTP commands (like Append) are NOT supported by the FTP Proxy.
Note: An explanation of FTP port and pasv modes can be found at http://www.slacksite.com/other/ftp.html