Laravel 5.1 Send mail to all users in foreach [GuzzleHttp\Exception\ClientException] Client error: 400

I'm trying to send an email to all the users in the database, but I'm getting the following error: [GuzzleHttp\Exception\ClientException] Client error: 400.

Here's my code:

$users = App\User::all();

foreach($users as $user) {
    $code = new App\Code();
    $code->code = str_random(10);
    $code->save();

    Mail::send('emails.code', ['code' => $code], function($message) use ($user)
    {
         $message->to($user->email)->from('foo.bar@gmail.com', 'Foo Bar')->subject('New code, new chances!');
    });
}

via Chebli Mohamed