In Gravity Forms Blacklist there are three types of list: Blacklist, White List, Email List.
The three lists are similar in interface so here just use Blacklist to do as demo.
When a list saved you may add item on the list edit page. You have two ways to add item, add manually enter or import by CSV file.
You may download the CSV template file to organize your own CSV file. Make sure only one column in each row of your CSV.
There is also an option to Export all items to CSV file.
Make sure what you enter is a valid email address when add item to email list. If by CSV then the column of every row should be a valid email address.
Email domain name only support adding manually
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