imap函数不适合我与PHP

我尝试用PHP访问我的gmail帐户，但我在第2行得到一个错误消息。Gmail中启用了IMAP，而没有启用POP。

$mbox = imap_open("{imap.gmail.com:993/ssl}", "email@gmail.com", "password");
echo "<h1>Mailboxes</h1>'n";
$folders = imap_listmailbox($mbox, "{imap.gmail.com:993}", "*");
if ($folders == false) {
    echo "Call failed<br />'n";
}
else {
    foreach ($folders as $val) {
        echo $val . "<br />'n";
    }
}
echo "<h1>Headers in INBOX</h1>'n";
$headers = imap_headers($mbox);
if ($headers == false) {
    echo "Call failed<br />'n";
}
else {
    foreach ($headers as $val) {
        echo $val . "<br />'n";
    }
}
imap_close($mbox);