FTPS: Choose various modes and options
It is important to specify whether the FTP connection uses Active or Passive mode. This is done by setting PassiveMode property to false or true. In Active mode, when the client establishes data connection, it just opens the port and waits for the server to connect. In Passive mode the server opens the socket, to which the client connects. Active mode usually doesn't work if the client is behind the NAT or firewall.
When using Passive mode, if the server is behind the firewall, it can report an incorrect address to connect to. In this case you need to set AdjustPasvAddress property to true - it will tell the client to use the server's known address instead of the (usually internal) address provided by the server.
If you need to use SSL/TLS (i.e. FTPS), see the corresponding how-to article.