在php中发送文件附件时，附件未打开

我使用此代码从表单向电子邮件发送附件，但我面临两个问题： 1-有时它工作，有时停止工作 2-当我在电子邮件中收到attachmet时，我可以看到大小为的附加文件，但它没有打开，对于word文档文件，它是打开的，但它是空的，对于图片、excel文件和pdf，也一样，任何人都可以帮助吗

<?php
// Email address to which you want to send email
$to = 'xxx@xxx.com';
$subject = $_POST['fname'];
//$message = nl2br($_POST["fname"]);
/*********Creating Uniqid Session*******/
$txtSid = md5(uniqid(time()));
$headers = "";
$headers .= "From: ".$_POST['fname']."<".$_POST['femail'].">\r\nReply-To:   
".$_POST['femail']."\r\n";
$headers .= "MIME-Version: 1.0\r\n";
$headers .= "Content-Type: multipart/mixed; boundary=\"".$txtSid."\"\r\n\n";
$headers .= "This is a multi-part message in MIME format.\r\n";
$headers .= "--".$txtSid."\r\n";
$headers .= "Content-type: text/html; charset=utf-8\n";
$headers .= "Content-Transfer-Encoding: 7bit\r\n\n";
//$headers .= $message."\r\n\n";
/***********Email Attachment************/
if($_FILES['attachment']['name'] != "")
{
    $txtFilesName = $_FILES['attachment']['name'];
    $txtContent = chunk_split(base64_encode(file_get_contents($_FILES['attachment']  
['tmp_name']))); 
    $headers .= "--".$txtSid."\r\n";
    $headers .= "Content-Type: application/octet-stream; name=\"".$txtFilesName."\"\n"; 
    $headers .= "Content-Transfer-Encoding: base64\n";
    $headers .= "Content-Disposition: attachment; filename=\"".$txtFilesName."\"\r\n\n";
    $headers .= $txtContent."\r\n\n";
}

// @ is for skiping Errors //
$flgSend=@mail($to,$subject,null,$headers);  
if($flgSend)
{
    echo "Email Sent SuccessFully, WelServ will contact you as soon as possible.<br/>you 
will be redirected in 5 seconds<br/>";
    echo "<script language='javascript'>window.setTimeout(function() 
{location.href='hire.php'}, 5000)</script>";

}
else
{
    $errorread=error_get_last(); 
    echo '$errorread';
    echo "Error in Sending Email, please try again,  you will be redirected in 5 
seconds!<br/>";
    echo "<script language='javascript'>window.setTimeout(function() 
{location.href='hire.php'}, 5000)</script>";
}

?>

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第x次：不要自己使用PHP的mail做这样的事情，而是使用类似PHPMailer或Swift-mailer的mailer类。zend mail呢？我对这些mailer不熟悉