protected function _validateAddrSpec($addr_spec)
    {
        $addr_spec = trim($addr_spec);

        // Split on @ sign if there is one.
        if (strpos($addr_spec, '@') !== false) {
            $parts      = explode('@', $addr_spec);
            $local_part = $this->_splitCheck($parts, '@');
            $domain     = substr($addr_spec, strlen($local_part . '@'));

        // No @ sign so assume the default domain.
        } else {
            $local_part = $addr_spec;
            $domain     = $this->default_domain;
        }

        if (($local_part = $this->_validateLocalPart($local_part)) === false) return false;
        if (($domain     = $this->_validateDomain($domain)) === false) return false;

        // Got here so return successful.
        return array('local_part' => $local_part, 'domain' => $domain);
    }