Login to Plesk via FTP fails: unable to determine IP address

Symptoms

1. FTP connection to the server cannot be established. FTP client returns the error:

   CONFIG_TEXT: 421 Service not available, remote server has closed connection

2. Error in /var/log/messages:

   PLESK_INFO: getaddrinfo 'wronghost.example.com' error: Name or service not known warning: unable to determine IP address of 'wronghost.example.com domain'

3. Hostname mentioned in the error is not reachable:

   # ping wronghost.example.com
   ping: wronghost.example.com: Name or service not known ping `wronghost.example.com`

Cause

Hostname misconfiguration: FTP server is unable to determine IP address of the server by hostname.

Resolution

Note: if you don't have root access to Plesk server via SSH, contact your hosting provider regarding the issue.