If you want to exclude a customer or group of customers from getting review requests, you will need to use customer exclusion filters.
There are two customer attributes that can be used for exclusions:
Country
Email
To do exclude customers from receiving requests, follow these steps:
Click on Configuration
Then select Settings
Once under Store Settings
Click on Exclusions
Under Exclude Customers, click on +Conditions
Now, choose which condition(s) you would prefer for your customer exclusion