How to configure secure FTP in Plesk for Linux?
FTP over SSL can be activated with following steps:
Allow using custom FTPS settings per IP address in Tools & Settings > Security Policy
Configure FTPS in Tools & Settings > IP addresses > Allow both secure FTPS and non-secure FTP connections.
Made sure that the following lines is present in
# common settings for all virtual hosts
# Authenticate clients that want to use FTP over TLS?
# Allow SSL/TLS renegotiations when the client requests them, but
# do not force the renegotations. Some clients do not support
# SSL/TLS renegotiations; when mod_tls forces a renegotiation, these
# clients will close the data connection, or there will be a timeout
# on an idle data connection.
# As of ProFTPD 1.3.3rc1, mod_tls only accepts SSL/TLS data connections
# that reuse the SSL session of the control connection, as a security measure.