Hello @Martin Thong Thank you for reaching out to us on Microsoft Q&A platform. Happy to help!
Based on the details provided, I understand that you are looking for a solution to receive email notifications for backup failures for 100+ subscriptions.
You need to create one notification rule (alert processing rule) per subscription to get notified on backup failures, you can use templates/scripts to automate this and run it for each subscription. This doc gives some options along with sample ARM templates https://learn.microsoft.com/azure/backup/move-to-azure-monitor-alerts#set-up-notifications-for-azure-monitor-alerts
Hope this helps. Please write back to us if you need further assistance!
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