php mail函数 subject乱码

<?php
/**
 * mail 功能
 */
function emailto($From, $To, $subject, $message)
{
   $headers  = "MIME-Version: 1.0/r/n";
   $headers .= "Content-type: text/html; charset=UTF-8/r/n";
   $headers .= "From: $From/nReply-To: $From/nX-Mailer: PHP/".phpversion();
   
   $bool = mail($To, encodeMIMEString ("UTF-8", $subject), $message, $headers);
   return $bool;
}
/**
 * 信件標題編碼
 */
function encodeMIMEString ($enc, $string)
{
   return "=?$enc?B?".base64_encode($string)."?=";
}