This deals with WordPress plugin development. Even if a user has not actually signed into WordPress, but has left a comment, WordPress remembers them from the last time. I wanted to toggle showing a "Subscribe To Newsletter" checkbox if they had already subscribed previously to a newsletter. I've already worked out the checkbox and it writes to another table storing the comment author's email when they post. But what is difficult is that I want to not show the checkbox if the user has already subscribed. It's easy enough to not show the checkbox if I had an actual email address, but I don't know how to retrieve the email address simply when the comment form is shown.

Note, using get\_currentuserinfo() does not apply here because the user is a commentor, not a blog article admin or author.

I need something where the user comes to a post they have not yet commented on. They may have commented on other posts, just not this one. In WordPress, you'll notice that it automatically knows this and assigns a Name and Mail field value through cookies.