I'm not sure if this would affect that but can you verify that the 'smart alerting' checkbox isn't selected for this email action? This might be supressing the incident ended email until the incident is confirmed.
Yes, what that basically does is it won't fire the email action after an incident starts until you manually go into the incidents dashlet and right click -> confirm the incident. It seems this includes the ending email as well as if any new incidents start you won't get the email with this enabled. Sometimes this is desirable but in your case I would turn this off.
Thanks James. That completely makes sense to me. May be I can jus disable it. But I have a question like if I keep smart alerting enable and if I confirm all incidents of this Incident from dashlet do I still get email notifications in future from this incident?
Once all existing incidents are confirmed, you'll get an email for the next time the incident fires. Then you'll have to confirm this new incident to receive any more. But yes confirming all incidents just changes the state of those incidents, you'll still receive the next one - it won't apply to future incidents or delete anything.