To do so, you need to comment out two lines in your proftod.conf file, namely <VirtualHost> and </VirtualHost>. The <VirtualHost> directive limit access to ftp on spesific ip or dns (like your.dns.com). The rest of your proftpd.conf file can remain the same.
Then connect to localhost. Here are the commands for the default ftp program:
Please post whatever comes out