Getting email addresses via while loop and sending php email

Question

I am attempting to send a message to all users on my site with the group of 5. However, the way I have this email form structured, I am getting my if statement response come back saying the email address was not filled in.

I'm trying to add the email address through a while loop like this..

while ($stmt->fetch()) {
            $to = $user_email;
}

I am sending the subject and message through my form via AJAX. I am not getting any errors from that. This is the part I get sent back to me onto my page..

 else {
    echo "Email Address was not filled out.";
}

What am I doing wrong for this to say an email address was not filled in? Also if I have more than one user's email address, would the way I have it work or would I need to structure the $to differently?

Here is the full code:

$subject = $_POST['subject'];
$message = $_POST['message'];


try {
    $con = mysqli_connect("localhost", "", "", ""); 
    if (mysqli_connect_errno()) { 
        printf("Connect failed: %s\n", mysqli_connect_error()); 
        exit(); 
    }
    $stmt = $con->prepare("SELECT id, email, username FROM users WHERE `group` IN (5)");
    if ( !$stmt || $con->error ) {
         // Check Errors for prepare
            die('User/Player SELECT prepare() failed: ' . htmlspecialchars($con->error));
        }
    if(!$stmt->execute()) {
            die('User/Player SELECT execute() failed: ' . htmlspecialchars($stmt->error));
    }
     $stmt->store_result();
} catch (Exception $e ) {
    die("User/Player SELECT execute() failed: " . $e->getMessage());
}
    $stmt->bind_result($userid, $user_email, $username);
while ($stmt->fetch()) {
            $to = $user_email;
}           
            $subject = 'Updated Status';
            $message = '';

            $from = "surveys@example.com";
            $Bcc = "surveys_check@example.com";

            // To send HTML mail, the Content-type header must be set
            $headers  = 'MIME-Version: 1.0' . "\r\n";
            $headers .= 'Content-type: text/html; charset=iso-8859-1' . "\r\n";

            // Additional headers
            //$headers .= 'To: ' .$to;//. "\r\n";
            $headers .= 'From: ' .$from. "\r\n";
            $headers .= 'Bcc: '.$Bcc. "\r\n"; 

            // Send the email
            //mail($to,$subject,$message,$headers);
            //if(mail($to,$subject,$message,$headers)){
              //   echo "Success";
            //} else { 
              //   print_r(error_get_last());
               //  echo "Fail";
            //}


            if (!empty($email)) { 
    if (filter_var($email, FILTER_VALIDATE_EMAIL)) { 

        //Should also do a check on the mail function
        if (mail($to, $subject, $message, $headers)) {
            echo "Your email was sent!"; // success message
        } else {
            echo "Mail could not be sent!"; // failed message
        }

    } else { 
        //Invalid email
        echo "Invalid Email, please provide a valid email address.";
    }

} else {
    echo "Email Address was not filled out.";
}

Answer 1

It looks like $email is not being defined. You could check for $to instead of $email in :

if (!empty($email)) { 
    ...
}

so:

if (!empty($to)) { 
    ...
}

For multiple recipients, use this:

$to .= $user_email . ',';

after defining $to = ''; before your while loop