寄信標題亂碼(outlook收信之類的)

//寄信
$mailtype='Content-Type:text/html;charset=utf8';
$mailFrom=$_POST['cn_email'];
$mailTo=xxx@xxx.com.tw';
$mailCC='link7311@gmail.com';
$mailBCC='';
$mailSubject=$_POST['cn_title'];
$mailSubject = "=?UTF-8?B?" . base64_encode($mailSubject) . "?=";//<---------要加這一行
$mailContent = "Content: ";
$mailContent .=nl2br($_POST['cn_content']);
$mailContent .= "<br>";
$mailContent .= "Name: ";
$mailContent .= $_POST['cn_name'];
$mailContent .= "<br>";
$mailContent .= "Phone: ";
$mailContent .= $_POST['cn_phone'];
$mailContent .= "<br>";
$mailContent .= "Company: ";
$mailContent .= $_POST['cn_company'];
$mailContent .= "<br>";
$mailContent .= "Email: ";
$mailContent .= $_POST['cn_email'];
$mailContent .= "<br>";
$maildata = "From:$mailFrom\r\n";
if ($mailCC != '') {
$maildata .= "CC:$mailCC\r\n";
}
if ($mailBCC != '') {
$maildata .= "BCC:$mailBCC\r\n";
}
$maildata .= "$mailtype";
mail($mailTo,$mailSubject,$mailContent,$maildata);