I am using ISPConfig 3.1.13 on Ubuntu 18.04 x64. I have configured two clients and fora each client, I have created 2 sites like site.domain1.com & domain1.com for client1 & so on. I have also created FTP accounts for each sites with domain root access. Whenever I try to upload some files using FileZilla, I get the error as 'Failed to retrieve directory listing' after a long waiting of 'Retrieving directory listing of "/web/customization/css". This happens every time even if I reboot the server. The server is hosted in Digital Ocean and there is no firewall behind the server network. Also, I have not enabled any firewall in the ISPC too. In the monitoring section, no errors or warnings displayed except 1 or more components needs an update (Ubuntu update) In the log, I found only these type of logs. Nov 25 08:27:31 domain.com pure-ftpd: ([email protected]) [INFO] New connection from 188.8.131.52 Nov 25 08:27:31 domain.com pure-ftpd: ([email protected]) [INFO] domain_admin_ftp is now logged in My Iptable rules show like this. iptables -S (ipv4) -P INPUT ACCEPT -P FORWARD ACCEPT -P OUTPUT ACCEPT I have even tried by enabling passive ports range to 30000 50000 in pure-ftpd.conf (Uncommented). But still same problem. Is this because the server uses private IP and public IP for networking? Please help me to resolve this problem.