php mail 题目乱码

php mail 标题乱码
$to = 'yangyingjieok@163.com';
$subject = "=?UTF-8?B?" . base64_encode('愚人节') . "?=";
$message = " 愚人节愚人节愚人节愚人节愚人节愚人节愚人节............... ";
mail($to, $subject, $message)

加上  base64_encode进行编码转换