Either you're at a small ISP and paypal doesn't care about a handful of customers that need to dig an email out of the spam folder, or you're at a large one and it won't have an effect because nobody else is reporting it
This doesn't hurt paypal but might annoy a small email hoster that might have to clean up your mess.
People use Paypal because they can't get around it. If you want to hurt them, help reduce their market share. Complain to the support of the service where you needed paypal, asking for better payment options (cite articles like this or whatever). That's what I do anyway, and doubly so when I know the owner. That they need to also offer paypal to get more customers, sure that's their risk (I make sure they're aware of it), but at least offer legit payment options as well