Laravel sending each e-mail multiple times

When a certain event is fired, my Laravel based app has to send exactly one transactional email to each user in a mailing list.

Here is the loop code:

$users = User::where('notifiable', 1)->get();

foreach($users as $user) {

    $info = [
        'email' => $user->email,
        'name'  => $user->name
    ];

    $data = [
        'message'   => 'Sample text'
    ];

    Mail::send(['emails.html.notification', 'emails.text.notification',], $data, function($message) use ($info) {
        $message
            ->to($info['email'], $info['name'])
            ->subject('example')
            ->from('admin@example.com','Example');
    });

}

Unfortunately, several users are receiving the same mail multiple times. I can't figure out what's happening:

• When redirecting the emails to log, I see exactly one mail for each user as expected;
• Every other events trigger emails to be sent to a single user. However, no one has received multiple emails from these events.

The app is using Sendinblue as an external SMTP service. Some hints I got:

• The hourly mail quota was very low -> the email were received 3 times (and the queue on Sendinblue was immediately filled)
• The hourly mail quota was raised 10x -> no more queues on Sendinblue, but now users are receiving the same email up to 7 times!

Apparently, queuing the email and setting a delayed event has solved the problem.

Now a new job is requested every 10 seconds.

$users = User::where('notifiable', 1)->get();

$counter = 0;

foreach($users as $user) {

    $payload = [
        'email' => $user->email,
        'name'  => $user->name,
        'message'   => 'Sample text'
    ];

    dispatch(new SendNotification($payload))
    ->delay(now()->addSeconds($counter * 10));

    $counter++;

}

Thanks for your support!