sudo vi /usr/local/etc/ddclient/ddclient.conf

daemon=300 # check every 300 seconds
 syslog=yes # log update msgs to syslog
 mail=root # mail all msgs to root
 mail-failure=root # mail failed update msgs to root
 ssl=no # use ssl-support. Works with ssl library // ssl=yes default

pid=/usr/local/var/run/ddclient/pid
 use=web
 server=dyndns.inwx.de
 protocol=dyndns2
 login=bhensler
 password=
 bernhard.hensler.net,www.bme-ravensburg.de

sudo /usr/local/sbin/ddclient -force
sudo rm /usr/local/var/run/ddclient/ddclient.cache

Autostart:
sudo cp -fv /usr/local/opt/ddclient/*.plist /Library/LaunchDaemons
sudo launchctl load /Library/LaunchDaemons/homebrew.mxcl.ddclient.plist