Metric alerts not sending email

already i have webhook for issues. I understood that, issues in sentry will be created for only new issues. In case of new events on existing issues, i am not getting webhook message.
but i am seeing one issue every 5 mins, sending one error message so i am getting for every 5 mins. somewhat i want to notifiy it via webhook. so i tried to create a metric alert.
in that, i have selected a timing window as “30 mins” you can refer the screen i am expecing a email from sentry that, it crossed threshold.

but i didn’t get anything.
in this case, i have doubt my email configuration but i received a week report sentry.
so it confirms that, no problem with email configuration.

but i don’t know the reason, why sentry metric alert is not working as per my expectation.
if anything i understood wrong. please inform me.

my sentry details,

  1. version - Sentry 21.2.0.dev00523a63
  2. authentication - basic username & password
  3. already webhook is configured as public integration
  4. i have configured internal integration also for this metric alert webhook (once i receive email, i planned to try with webhoo using internal integration)