This simple script should be inserted into line 54 of wp-comments-post.php to block comments based on email addresses.

block_comments_by_email.php

// Goes after this section below
$comment_author       = ( isset($_POST['author']) )  ? trim(strip_tags($_POST['author'])) : null;
$comment_author_email = ( isset($_POST['email']) )   ? trim($_POST['email']) : null;
$comment_author_url   = ( isset($_POST['url']) )     ? trim($_POST['url']) : null;
$comment_content      = ( isset($_POST['comment']) ) ? trim($_POST['comment']) : null;

// WordPress Block Commenters by email
$black_list = array( 
  "guert84****@gmail.com",
  "test@dillonhafer.com"
);

if (in_array($comment_author_email, $black_list)) {
  $comment_author_email = null;
}