You might face a situation like, an alarm was violated but no alerts have been triggered. All alarms are working fine and sending emails even that particular alarm was working for a couple of days.
The first and foremost things is you need to check, the number of notification sent for that particular alarm.
While creating an alarm you will configure the limit number of alerts for a violation, based on the configuration Down and Up alerts will be triggered.
When the violation occurs the down alert emails will be triggered based on the configuration. If it reached the maximum limit it stops sending the alerts and it will not trigger emails for the new violations.
To resolve this you have a couple of options:
1. Need to rectify the problem so that the problem will be resolved and the UP alert email will be sent also the Notification send will be reset back to 0.
2. Can Reset the alarm so that the Notification send will be reset back to 0.