For those who are wondering why ProFTPd (no valid server configured) is not starting , here is your solution :-).
I was struggling to get this working in one of the server (see below for the error) but no luck even after several repeats of usual tips, ie., restart/reinstall (/etc/init.d/proftpd restart) – simply nothing.
This is the error I was getting each time when I try to start ProFTPd:
Checking syntax of configuration file
– warning: unable to determine IP address of ‘example.com′
– error: no valid servers configured
– Fatal: error processing configuration file ‘/etc/proftpd.conf’
Following solution works with all Debian based Linux Distribution. Others, placement of the config files may vary with other Linux distribution, please find the correct path to the config file(s) that I have mentioned in the solution.