<?php
include_once("mime.inc");
$mm = new MIME();
$to = "customer@263.net";
$subject = $mm->encode("商城","gb2312"); // 编码
$msg = "注册会员成功<br>";
$msg .= "会员名：wayne<br>";
$msg .= "密码：wayne</font>";
$headers = "From: webmaster@263.net\r\nContent-Type: text/html; charset=gb2312\r\n";
mail("$to", "$subject", "$msg", "$headers");    
?>
进行编码以后，中文问题解决。