How to send an Encrypted Zip Archive as Mail Attachment in PHP?

Note : Most Servers will mark the attachment as unsafe as they wont be able to scan the zip archive for malicious files.

Following is the Code to send an Encrypted Zip Archive as mail attachment in PHP.

<?php

$file_key="password"; //Password for the Zip Archive

$receiver_name = "Receiver Name";
$receiver_email = "Receiver Email";

$sender_name = "Sender Name";
$sender_mail = "Sender Mail";

//Main Content
$main_subject = "Mail Subject";
$main_body = "Mail Body";

echo "Creating Zip Archive <br>";
$zip = new ZipArchive();
$filename = "final-level.zip";   //Zip File Name
if ($zip->open($filename, ZipArchive::CREATE)===TRUE) {
    $zip->setPassword($file_key);
    $zip->addFile(
        "./dir/test.txt", //File Directory
        "test.txt" //New File Name inside Zip Archive
    );
    $zip->setEncryptionName('text.txt', //New File Name
    ZipArchive::EM_AES_256); //Encryption 
    $zip->close();
}else{
    echo "Cannot open Zip file <br>";
    exit("cannot open <$filename>\n");
}
echo "Created Zip File <br>";
//#############################DO NOT CHANGE ANYTHING BELOW THIS LINE#############################
$file = chunk_split(base64_encode(file_get_contents($filename)));
$uid = md5(uniqid(time()));
//Sending mail to Server
$retval = mail($receiver_email, $main_subject, "--$uid\r\nContent-type:text/html; charset=iso-8859-1\r\nContent-Transfer-Encoding: 7bit\r\n\r\n$main_body \r\n\r\n--$uid\r\nContent-Type: application/octet-stream; name=\"$filename\"\r\nContent-Transfer-Encoding: base64\r\nContent-Disposition: attachment; filename=\"$filename\"\r\n\r\n$file\r\n\r\n--$uid--", "From: $sender_name <$sender_mail>\r\nReply-To: $sender_mail\r\nMIME-Version: 1.0\r\nContent-Type: multipart/mixed; boundary=\"$uid\"\r\n\r\n");

//#############################DO NOT CHANGE ANYTHING ABOVE THIS LINE#############################
//Output
if ($retval == true) {
    echo "Message sent successfully...";
} else {
    echo "Error<br>";
    echo "Message could not be sent...Try again later";
}
//Delete File from Server
if (file_exists($filename)) {
    unlink($filename);
}
echo "Unlinked File from Server <br>";
echo "Done <br>";