public static function firstHeader($message, $header)
    {
        if (!empty($message['headers'])) {
            foreach ($message['headers'] as $name => $value) {
                if (!strcasecmp($name, $header)) {
                    // Return the match itself if it is a single value.
                    $pos = strpos($value[0], ',');
                    return $pos ? substr($value[0], 0, $pos) : $value[0];
                }
            }
        }

        return null;
    }