How to Blacklist Commenters in WordPress
Step 1) Log in to the WordPress Dashboard
Step 2) Click Settings on the left hand menu
Step 3) Click Discussion on the left hand menu
Step 4) Scroll down to “Comment Blacklist” where you can ban a commenter by their Name, E-mail, URL, IP Address, or content of the comment.
Step 5) Enter what you require to stop troublesome commenters, then, scroll down and click Save Changes to confirm.