php函数 imap_open使用问题

在登陆页面输入相应信息，转到如下代码处理，不能跳转到lookmail.php。怎样解决？求大神指教
<?php
session_start();
$hostname="{".$_POST[hostname].":110/pop3}INBOX";
$username=$_POST[username];
$userpwd=$_POST[userpwd];
if(!$mbox=@imap_open("{pop3.czk.cn:110}","$username","$userpwd")){
echo "<script charset='utf-8'>alert('登录失败!');window.location.href='index.php';</script>";
}else{
session_register("host");
session_register("user");
session_register("pwd");
$_SESSION[host]=$hostname;
$_SESSION[user]=$username;
$_SESSION[pwd]=$userpwd;
imap_close($mbox);
echo "<script charset='utf-8'>window.location.href='lookmail.php';</script>";
}
?>