$email= "example@something";

$host = 'localhost';

$dbname = 'users';

$username = 'root';

$password = '';

    $conn = new PDO("mysql:host = $servername;dbname =

$dbname",$username,$password);

    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    $query = $conn->prepare("SELECT email FROM users.registered_users  WHERE

email='$email'");

$query->execute(array($email));

$row = $query->fetch(PDO::FETCH_BOTH);

if($query->rowCount() > 0) {

echo "email found";

} else {

  echo "email not found";

}