For every email, I would send an abuse complaint to the registrar on their whois lookup, which right now is Markmonitor [0]. I have done this to get one spammy website's emails shut off before, when they weren't including unsubscribe links. Of course they were back on their same bullshit weeks later, but I was able to unsubscribe successfully.

IDK, maybe PayPal is too powerful or whatever they're doing here is technically legal, but it is worth a shot.

[0] https://www.markmonitor.com/legal/abuse-policy