When paypal sends a notification to HikaShop, it waits to receive a 200 HTTP request at the end of the hikashop processing. If such response is received, then that's it. If another response is received by paypal, it will requeue the notification in order to send it later on until it succeed and does that 10 times.
Since you're getting all these emails, it means that the hikashop process goes to the end but that your website still doesn't send back a 200 HTTP response to paypal. The thing to do in that case is to open the notification URL on your website to see if you have any errors. It's most likely that something else on your website is triggering an error (template, plugin, module...) on that notification page and that will help us find the culprit.
Could you give an access to your website, deactivate the IP check in the paypal plugin so that we ca see the problem ?