PHP mail() and charset encoding question

<?php
/*
MyMailer class
Copyright (C) 2007 Shih Yuncheng <shirock@educities.edu.tw>
This library is licensed under GNU Lesser General Public License.
*/
class MyMailer {
    private static function waitSmtpResponse(&$sh, $code) {
        echo ($response = fgets($sh));
        if (strncmp($response, $code, 3)) {
            echo $response;
            return self::smtpFalse($sh);
        }
        return true;
    }

    private static function smtpFalse(&$sh) {
        fclose($sh);
        return false;
    }

    public static function mail($To, $Subject, $message, $additional_headers=false) {
        $headerTable = array('To', 'Subject');

        $smtpServer = get_cfg_var('SMTP');
        if (empty($smtpServer))
            return false;

        if (!($mailFrom = get_cfg_var('sendmail_from'))) {
            $headers = explode("\n", $additional_headers);
            foreach ($headers as $header) {
                if (preg_match('/^From: ([^\b]+)/', $header, $matches))
                    $mailFrom = $matches[1];
            }
            if (empty($mailFrom))
                return self::smtpFalse($fsock);
        }

        if (!($fsock = fsockopen('tcp://'.$smtpServer, get_cfg_var('smtp_port'),
            $errno, $errstr)))
        {
            return false;
        }
        if (!self::waitSmtpResponse($fsock, '220'))
            return false;

        fwrite($fsock, "Helo {$smtpServer}\r\n");
        if (!self::waitSmtpResponse($fsock, '250'))
            return false;

        fwrite($fsock, "Mail from: {$mailFrom}\r\n");
        if (!self::waitSmtpResponse($fsock, '250'))
            return false;

        $rcptSet = explode(',', $To);
        foreach ($rcptSet as $rcpt) {
            fwrite($fsock, "Rcpt to: {$rcpt}\r\n");
            if (!self::waitSmtpResponse($fsock, '250'))
                return false;
        }

        fwrite($fsock, "Data\r\n");
        if (!self::waitSmtpResponse($fsock, '354')) //354 Enter mail

            return false;

        foreach ($headerTable as $cmd)
            fwrite($fsock, "${cmd}: {$$cmd}\r\n");
        if ($additional_headers)
            fwrite($fsock, $additional_headers);
        fwrite($fsock, "\r\n");

        fwrite($fsock, $message);
        fwrite($fsock, "\r\n.\r\n");

        fwrite($fsock, "Quit\r\n");
        fclose($fsock);
    }
}
?>

<?php
require 'MyMailer.php';

$mailTo = 'your@example.com'; // 請自行替換有效的收件地址

$message = 'test 測試';
$subject = 'TEST 測試';
$headers = 'Content-type: text/plain; charset="big5"' . "\r\n";
$headers .= 'From: my@example.com' . "\r\n"; // 請自行替換寄件地址


mail($mailTo, $subject, $message, $headers);
MyMailer::mail($mailTo, $subject, $message, $headers);
?>

<?php
//資料皆為utf-8編碼

$messageHeaderMap = array(
    'Subject'   =>  '中文標題測試',
    'From'      =>  '許功蓋 <you@example.com>'
);

$charset = 'utf-8';
$messageEncoding = 'base64';
$headerFormat = '=?' . $charset . '?' . $messageEncoding[0] . '?%s?=';

$headers = '';
foreach ($messageHeaderMap as $k => $v) {
    $headers .= $k . ': ' . sprintf($headerFormat, base64_encode($v)) . "\r\n";
}
$headers .= 'Content-type: text/plain; charset=' . $charset . "\r\n";

$message = '中文內容測試';

MyMailer::mail(
    'my@example.com',
    sprintf($headerFormat, base64_encode($messageHeaderMap['Subject'])),
    $message,
    $headers
);
?>