'Send Notification email to client' checkbox on case layout is not visible

Hi

I am not able view 'Send Notification email to Client' Checbox' on edit page of case Layout.

I have enabled the Email Notification Checkbox on Layout Properties in the page layout. And PageLayout Assignments are properly assigned. 

But Still not able to view that checkbox on the Case Page Layout. We do have case auto-response rule to send an email on case creation. This checkbox need to be available in order for the Auto-response rule to work. 

Can anyone suggest any solution? I am not able to find any solution out there

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