PHP Mail Return-Path not bouncing back

I'm trying to test if the return-path will bounce back on my gmail, but not.

I'm testing to send it to my email ([email protected]): it works!
And send to unknown email ([email protected]): it didn't bounce back.

Here's my code

<?php
$message = '
    <html>
    <head>
        <title>Sample Email</title>
    </head>
    <body>
        Sample Email
        <br /><br />
        <a href="http://asd.com/[email protected]">Click here to Unsubscribe</a>
    </body>
    </html>
';

$sender = "[email protected]";
$email_address = "[email protected]";
$subject = "Testing Email";
$template_name = "Sample Email";

$headers  = 'MIME-Version: 1.0' . "\r\n";
$headers .= 'Content-type: text/html; charset=iso-8859-1' . "\r\n";
$headers .= 'Return-Path: [email protected]' . "\r\n";
$headers .= 'From: '.$sender.'' . "\r\n";

if(mail($email_address, $subject, $message, $headers, '[email protected]'))
    echo "{$i}. {$email_address} - <span style='color:green'>Successfully</span> Sent [{$template_name}]<br />";
else
    echo "{$i}. {$email_address} - <span style='color:green'>Unsuccessfully</span> Sent [{$template_name}]<br />";

Solution

You have two solutions to this issue: First one is leave blank in the php.ini configuration file the "sendmail_from" variable. This way you could add the additional parameters in the mail function like you have in your code.

The second approach, is set "sendmail_from" in php.ini if you want to have always the same "Return-Path" for every email.