[xurshudyan]

Queued mailables ignore #[DeleteWhenMissingModels] and #[FailOnTimeout] (and the $deleteWhenMissingModels / $failOnTimeout properties), because SendQueuedMailable doesn't copy them from the mailable.

#[DeleteWhenMissingModels]
class OrderShipped extends Mailable implements ShouldQueue
{
    use Queueable, SerializesModels;

    public function __construct(public Order $order) {}
}

Mail::to($user)->later(now()->addMinutes(15), new OrderShipped($order));

If the order is deleted before the mail is sent, the job fails with a ModelNotFoundException and ends up in failed_jobs instead of being deleted. With #[FailOnTimeout], a mail that timed out on a slow SMTP server is retried anyway, so the customer can get it twice.