FTP passive mode require some or all unprivileged (1024-65534) ports to be accessible by the world. By default Plesk does not add a rule for these ports, so passive mode does not work. To enable passive mode we need to edit the ProFTPD (FTP server used by Plesk) configuration. Edit the config file (located here: /etc/proftpd.conf) with your favorite shell editor (like nano or vim). Find the <global> section and add the following rule between the <global> and </global> tags: