My old company provides satellite access to the US internet backbone. The cost is way more than a US company would pay, but third world countries don't have the infrastrusture to match the speed. Anyway, because of the overabundance of spam, we require our customers to register their mail servers and SMTP is only allowed from those mail servers. This has cut down spam complaints significantly. That's not to say it doesn't happen, but when a complaint comes in, we know who to contact to stop it. If it continues, we cut all mail from that address.