梨邮件“无法找到驱动程序SMTP类”找不到文件，即有(Pear Mail “Unable to fi

我的VPS运行的CentOS 5.3。我已经安装了梨，Mail和Net_Mail。当我尝试发送邮件时，我收到“无法找到驱动程序SMTP类”。我通过Mail.php看，发现我需要我的梨目录，其中有一个内部“邮件/ smtp.php”。我验证了PHP的包括目录，我重置所有烫发通过CHOWN到Apache。我检查输入chmod，而且都是644。

我的代码：

    $from = "Admin <admin@myemail.com>";
$to = "New User <".$email.">";
$subject = "Welcome to MyEmail!";
$body = "Thanks for choosing <MyEmail>! We strive to provide 24/7 email service and support. If you have ANY issues, concerns, etc, please reply to this email, or simply compose a new one to: myemail@email.com !";
$host = "localhost";
$username = "username";
$password = "password"; 
$headers = array ('From' => $from,
    'To' => $to,
    'Subject' => $subject);
$smtp = Mail::factory('smtp',
    array ('host' => $host,
    'auth' => true,
    'username' => $username,
    'password' => $password));
if (PEAR::isError($smtp)) {
    echo("<p>" . $smtp->getMessage() . "</p>");
}
$mail = $smtp->send($to, $headers, $body);
if (PEAR::isError($mail)) {
    echo("<p>" . $mail->getMessage() . "</p>");
} else {
    echo("<p>Message successfully sent!</p>");
}