Mailgun API works only with one email

Question

I'm making email subscription form with PHP and Mailgun API, but I only get email to my main email address which I used for account creation at mailgun.com. When I fill the form with that email, I get the confirmation letter, but it doesn't work with other emails. Why is so? This is the code:

Init file:

<?php
require_once 'vendor/autoload.php';

define('MAILGUN_KEY', 'key-2ce40f5e23c90b0d666f3e....');
define('MAILGUN_PUBKEY', 'pubkey-8cf7125996....');

define('MAILGUN_DOMAIN', 'sandboxc03eaee7674c4a9094ffa8d61845ddf5.mailgun.org');
define('MAILING_LIST', '[email protected]');
define('MAILGUN_SECRET', '...');

$mailgun = new Mailgun\Mailgun(MAILGUN_KEY);
$mailgunValidate = new Mailgun\Mailgun(MAILGUN_PUBKEY);
$mailgunOptIn = $mailgun->OptInHandler();
 ?>

Main index.php file:

<?php
require_once 'init.php';


if(isset($_POST['name'], $_POST['email']))
{
    $name = $_POST['name'];
    $email = $_POST['email'];

    $validate = $mailgunValidate->get('address/validate', [
        'address' => $email
    ])->http_response_body;

    if($validate->is_valid)
    {
        $hash = $mailgunOptIn->generateHash(MAILING_LIST, MAILGUN_SECRET, $email);

        $mailgun->sendMessage(MAILGUN_DOMAIN, [
            'from'      => '[email protected]',
            'to'            => $email,
            'subject'   => 'Please confirm your subscription to us',
            'html'      => "Hello {$name}<br><br>You signed up to our mailing list. Please confirm below"
        ]);

        $mailgun->post('lists/' . MAILING_LIST . '/members', [
            'name'              => $name,
            'address'               => $email,
            'subscribed'    => 'no'
        ]);

        header('Location: http://localhost:8888/exam/index.php');
    }

}
?>

Answer 1

You are using sandboxc03eaee7674c4a9094ffa8d61845ddf5.mailgun.org Sandbox subdomain for sending an email.

You should get an error like:

Error: Sandbox subdomains are for test purposes only. Please add your own domain or add the address to authorized recipients in Account Settings.

To send multiple emails, you have to create your own domain first. You can create domain from here

Make sure your domain is verified.If your domain is unverified then you will get an error like:

Error: The domain is unverified and requires DNS configuration. Log in to your control panel to view required DNS records.