Hi,
HikaShop and the akeebasubs plugin allow to set subscription level on a product, and then when paying through HikaShop the subscription is created.
Generally the plugin paypal recurring is used, because the subscriptions needs to be set a recurring subscriptions.
Then each recurring period, after the payment is made, we send the information to akeeba subscription to create a new subscription, and a new order is created in HikaShop, because this order is created, an email is sent.
In your case, if you don't use recurring subscriptions and so don't use paypal recurring, the subscriptions are managed in Akeeba subscriptions, so HikaShop don't have to send any emails, because it had no more informations about this subscriptions.