notification_interval stands for time units before nagios re-notifiying the service is still at a non-ok status
And if you dont like receiving email alerts if a host goes down during the weekend change the
to the days you want to receive the notifications...
I remind you im not a Guru on Nagios... just saying what i may think it its...
this is how i have my some hosts definition on hosts.cfg, it might help you cause i dont get 1000 emails like you do
use generic-host ; Name of host template to use