Hi @rupesh adhikari ,
notification email are sent using a standard address (not a personal one) so if a customer replies to a notification email it will be managed through a mail handler that create a comment in the related ticket.
If you are watcher and the notification scheme has been configured so that watchers receive notification for a comment you will be notify too.
Hope this helps,
You should atleast have Standard Subscription to edit the Notification Scheme in Jira associated for the Project.
In Notification Scheme associated for the Project, add the role (Preferably Issue Roles such as Assignee) you are in and you will be able to get the notification when user comments on an issue
Here's the reference