从Windows系统，邮件可以正常发送，但是在托管到centos中后，邮件以加密格式发送

Question

从Windows系统（本地）运行正常，但是在托管到centos中后，邮件以加密格式发送。我正在使用以下代码发送邮件。

$boundary = md5("sanwebe");

    $headers = "MIME-Version: 1.0\r\n"; 
    $headers .= "From:".$from_email."\r\n"; 
    $headers .= "Reply-To: ".$from_email."" . "\r\n";



    $headers .= "CC: ".$cc."" . "\r\n";
    $headers .= "Content-Type: multipart/mixed; boundary = $boundary\r\n\r\n"; 

    $body = "--$boundary\r\n";

    $body .= "Content-Type: text/html; charset=ISO-8859-1\r\n";

   $body .= "Content-Transfer-Encoding: base64\r\n\r\n"; 
    $body .= chunk_split(base64_encode($message)); 




    //attachment
    if (file_exists($file_name)){

        $body .= "--$boundary\r\n";
        $body .="Content-Type: $file_type; name=".$file_name."\r\n";
        $body .="Content-Disposition: attachment; filename=".$file_name."\r\n";         
        $body .="Content-Transfer-Encoding: base64\r\n";
        $body .="X-Attachment-Id: ".rand(1000,99999)."\r\n\r\n"; 
        $body .= $encoded_content; 

    }


$sentMail = @mail($recipient_email, $subject, $body, $headers);

Ouput Mail是：

8de2a431c506316063ec3a4044192e46
PGh0bWw+PGJvZHk+PHN0cm9uZz5EZWFyIFNpci9NYWRhbSw8L3N0cm9uZz4gPGJyIC8+DQo8YnIg
Lz4NCgkJIEluc3RydW1lbnQgOiBHQy8wMiwgc2VyaWFsX251bWJlciA6IEMxMjA5NTMwMjQ2Nywg
bWFrZSA6U2hpbWFkenUgIG1vZGVsIDpHQyAyMDEwIFBsdXMtIEluc3RydW1lbnQgaXMgYnJlYWtk
b3duIFBsZWFzZSBhbGxvdCBzZXJ2aWNlIFBlcnNvbiA8YnIgLz4NCjxiciAvPg0KQmVzdCBSZWdh
cmRzPGJyIC8+DQpBZG1pbiw8YnIgLz4NCiAgQWRtaW4sPGJyIC8+DQpWaW10YSBMYWJzIExpbWl0
ZWQuPC9ib2R5PjwvaHRtbD4=