I have a fresh install of nagios 3.0.3 running on Ubuntu Server 8.0.4. Nagios runs as expected, given not a lot of configuration is needed to do so, but I am struggling to get the email notification to work. I have installed mailx and can send mail via the command line, but I do not know what else I need to configure to receive notifications at an external address. I have a contact setup with just a name and email address in nagios, but am at a loss after that.
Issue was in commands.cfg. Though I had altered the notfy-host-by-email and notfy-service-by-email commands to use mailx, I did not append /usr to the beginning of the path. Email notifications are now being delivered.