How to check for a duplicate email address in PHP, considering Gmail (user.name+label@gmail.com)

Question

How can I check for duplicate email addresses in PHP, with the possibility of Gmail\'s automated labeler and punctuation in mind?

For example, I wan

Answer 1

function normalize($input) {
     $input = str_replace('.', '', $input);
     $pattern = '/\+(\w+)@/';
     return preg_replace($pattern, '@', $input);
}