Hi @Ravi Bhushan ,
You can follow the official documentation here:
How to create notification subscriptions
https://learn.microsoft.com/en-us/system-center/scom/manage-notifications-create-subscriptions?view=sc-om-2019
Here's also another guide to help you get started:
BEST PRACTICES: E-MAIL NOTIFICATION SUBSCRIPTIONS (SCOM 2012)
http://www.opsconfig.com/best-practices-e-mail-notification-subscriptions
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Best regards,
Leon