E-mail notifications / smtp question


I am trying to set up e-mail notification on services / hosts. Here’s what my config file looks like:

define contact{
contact_name nagiosadmin ; Short name of user
use generic-contact ; Inherit default values from generic-contact template (defined above)
alias Nagios Admin ; Full name of user
host_notifications_enabled 1
service_notifications_enabled 1
host_notification_period 24x7
service_notification_period 24x7
host_notification_options u
service_notification_options u,c
host_notification_commands notify-host-by-email
service_notification_commands notify-service-by-email
email xxx@xxx.com ; <<***** CHANGE THIS TO YOUR EMAIL ADDRESS ******

Under notifications, it says notification-service-by-email “ran”, and for the correct contact. Do any of other config files need to be changed? Also, where do I go to set up the smtp information so that the notification actually gets sent out? I am unsure if it is something within nagios, or on my machine, in which that case, I am running Ubuntu 7.10.