This handles WordPress wordpress plugin development. Even when a person hasn't really signed into WordPress, but has said, WordPress takes note of them in the before. I needed to toggle showing a "Sign Up For E-newsletter" checkbox when they had already activated formerly to some e-newsletter. I have already exercised the checkbox also it creates to a different table storing the comment author's email once they publish. But what's difficult is the fact that I wish to not show the checkbox when the user has activated. It is not difficult enough not to show the checkbox basically had a real current email address, but I'm not sure how you can retrieve the e-mail address simply once the comment form is proven.

Note, using get_currentuserinfo() doesn't apply here since the user is really a commentor, not really a blog article admin or author.

I want something in which the user involves a publish they haven't yet said on. They might have said on other posts, simply not that one. In WordPress, you'll find that it instantly knows it and assigns a Title and Mail area value through snacks.

You may have the ability to do this using get_comments, it returns an assortment using the key comment_author_email.

Essentially you'd need to loop through all of the comments to any or all the posts, retrieve all emails after which check it against your e-newsletter data.

More details concerning the syntax (and possible options) are available here: http://codex.wordpress.org/Function_Reference/get_comments

Here is a routine I've exercised, but possibly it can be done better through something within the WordPress codex?

function getCommentAuthorEmail() {
global $user_level;

  get_currentuserinfo();
  if($user_level > 0) { //if signed into wordpress as admin or author
    return ''; //don't provide anything
  }

  $sEmail = '';
  try {
    foreach($_COOKIE as $sKey => $sVal) {
      if (strpos(' ' . $sKey, 'comment_author_email')>0) {
        $sEmail = urldecode($sVal);
        break;
      }
    }
  } catch (Exception $e){}
  return $sEmail;
}