For our application. Pgwal was filled until 100%. Although the alert was configured, we didn't get the alert email.
We have tested with other Applications by decreasing the threshold values. Still we were not getting alerts.
Configuration of Alarms/notifications/channels/template was incorrect. Issue - Whenever adding more than one channel in Alert configuration page, it stopped working. We removed the additional channel and kept only one channel. Now it is working fine.
Test by creating another notification/channel/alarm and using the default message template.