Comment 2 for bug 126130

The specific error appears to be related to the use of getaddrinfo, perhaps dependant on particular networking or name server configurations. A locally reproduced postinst error is:

Setting up proftpd (1.3.0-21ubuntu1) ...
 * Starting ftp server proftpd
 - IPv4 getaddrinfo 'frigga' error: Name or service not known
 - warning: unable to determine IP address of 'frigga'
 - error: no valid servers configured
 - Fatal: error processing configuration file '/etc/proftpd/proftpd.conf'