FTP via FileZilla Prompts for Unknown Security Certificate

Plesk Servers > FTP
Issue
When connecting to your Managed.com hosted FTP accounts using the FileZilla FTP client, you receive a prompt regarding an Unknown SSL Certificate, as below:
 
 
AND/OR you will see the following in your connection window:
 
Status:	Connecting to (IP Address)...
Status:	Connection established, waiting for welcome message...
Status:	Initializing TLS...
Status:	Verifying certificate...
Status:	TLS connection established.
Status:	Connected
Status:	Retrieving directory listing...
Command:	PWD
Response:	257 "/" is current directory.
Command:	TYPE I
Response:	200 Type set to I.
Command:	PASV
Response:	227 Entering Passive Mode (IP, etc).
Command:	LIST
Response:	534 Protection level negotiation failed.
Error:	Failed to retrieve directory listing
Error:	Connection closed by server
 
Cause:
This is due to an update in the Filezilla client (3.10.0.1) that defaults connections to "Use explicit FTP over TLS if available". This only happens if you have your FTP connections saved in the Site Manager (File > Site Manager).
 
Resolution:
  1. Click on File > Site Manager.
  2. In the Encryption field choose Use Plain FTP.
  3. Click Connect to connect to your Managed.com hosted FTP account.
 

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