Magneto have default feature call Wishlist.
From this wishlist feature you can ad product to wishlist and order later & you can share this wishlist to you Friends & family. Now the problem is when a customer share the wishlist then there is a text area filed appear, where customer can give unlimited number of email & send them. If customer is not fraud then there will be no problem. But if customer is fraud and want to harm your account then this could be problem for your system.
In details given below.
Customer shareable wishlist example.
If customer click on share then the following page will appear.
Look here is an text area filed where separated by commas instruction shows, if customer give thousand of wrong email address for make your system harm, then you will be in hard trouble for mail delivery system. Your mail bounce rate will be high, if you use paid service then they can disable your account account. If it is Amazon ses then your account will be in big trouble.
There is a section in admin panel about wishlist settings, but where you can only enabled or disabled wishlist & change the template only.
It’s seems a hole in magento, so you need to fill it up in your system by custom code. Thanks.