Adding an email field to comment forms
I think you can make this work as follows:


In the Permissions settings via admin/people/permissions, ensure ANONYMOUS USER can View comments, Post comments, and Subscribe to comment notifications
In the Comment Notify settings via admin/config/people/comment_notify, ensure comment notification is enabled for the content type(s) you care about 
For each content type you care about, e.g. for Basic page via admin/structure/types/manage/page, expand the Comment settings tab in the vertical menu at the bottom of the page and ensure "Anonymous commenting" is set to Anonymous posters must leave their contact information