protected function _isGroup($address)
    {
        // First comma not in quotes, angles or escaped:
        $parts  = explode(',', $address);
        $string = $this->_splitCheck($parts, ',');

        // Now we have the first address, we can reliably check for a
        // group by searching for a colon that's not escaped or in
        // quotes or angle brackets.
        if (count($parts = explode(':', $string)) > 1) {
            $string2 = $this->_splitCheck($parts, ':');
            return ($string2 !== $string);
        } else {
            return false;
        }
    }