We faced a case assignment rule email sending issue in the past on our one sandbox and contacted with support. They fixed that using a critical update.
Update Name: Stop Automated Field Updates from Suppressing Email Notifications
Update Summary: This update stops processes, workflow rules, and Apex triggers from suppressing email notifications.
Now we are facing same issue in another sandbox but we unable to find the critical update in another sandbox. How can we find that critical update? Is there a way around so that I can activate that critical update in our another sandbox?