Export a List of Commenter Email Addresses From Your WordPress Blog
This is a simple way to get a list of all of the email addresses of anyone who has commented on your WordPress blog. Open up phpMyAdmin and select your database. Then click on the Query tab and run this:
SELECT DISTINCT comment_author_email FROM wp_comments WHERE comment_approved = '1'
This will generate a list of all the email addresses of commenters where the comment has been approved with no duplicates. Now you can click “Check All” and then “Export” under the query results operations section, as shown below:
You’ll be able to select from several different file types, including .csv, .doc, .pdf, .xml, and a few others.