PHP mail() not sending emails on mdbgo.io

    <?php
    require_once 'connection.inc.php';

    $subject = $_POST['subject'];
    $body = $_POST['body'];
    // Tried different versions of this first:
    $headers = "From: Newsletter No Reply <noreply@newsletter.mdbgo.io>\n";
    $headers .= "Reply-To: Newsletter <news@newsletter.mdbgo.io>\n";
    $headers .= "Content-Type: text/plain; charset='iso-8859-1'\n";
    $headers .= "Content-Transfer-Encoding: 8bit\n";

    // Tried this:
    // $headers = "From: Newsletter No Reply <noreply@newsletter.mdbgo.io>\r\n";
    // $headers .= "Reply-To: Newsletter <news@newsletter.mdbgo.io>\r\n";
    // $headers .= "X-Mailer: PHP/" . PHP_VERSION;

    // Tried this:
    // $headers = array("From: noreply@newsletter.mdbgo.io",
    //     "Reply-To: news@newsletter.mdbgo.io",
    //     "X-Mailer: PHP/" . PHP_VERSION;
    // );
    // $headers = implode("\r\n", $headers);

    // Tried this:
    // $headers = "From: noreply@newsletter.mdbgo.io" . "\r\n";
    // $headers .= "MIME-Version: 1.0" . "\r\n";
    // $headers .= "Content-type:text/html;charset=UTF-8" . "\r\n";

    // Tried this:
    // $headers[] = 'MIME-Version: 1.0';
    // $headers[] = 'Content-type: text/html; charset=iso-8859-1';
    // $headers = implode("\r\n", $headers);

    // Lastely tried this:
    // $headers = array(
    //     "From: noreply@newsletter.mdbgo.io",
    //     "Reply-To: news@newsletter.mdbgo.io",
    //     "Content-Type: text/plain; charset=iso-8859-1",
    //     "Content-Transfer-Encoding: 8bit"
    // );
    // $headers = implode("\r\n", $headers);

    // Rest of my code:
    $query = "SELECT * from $table";
    $result = $dbc->query($query)
        or die ("Error querying database... " . $dbc->error);

    while ($row = mysqli_fetch_array($result, MYSQLI_BOTH))
    {
        $first_name = $row["first_name"];
        $last_name = $row["last_name"];
        $email = $row["email"];

        $message = "Dear $first_name $last_name, \n $body";

        if(mail($email, $subject, $message, $headers)){
            echo "Email sent to: $email";
        }
        else {
            echo "MESSAGE: Failed to send email to: $email";
        }
    }
    ?>