Interesting - For about six months or so, I was getting hammered with spam that mostly originated with Yahoo. No address was valid (after a while I checked a couple, figured it couldn't hurt at that point, and they all came back unanswerable), and when I contacted Yahoo directly, they claimed they could do nothing about it. They said that their domain name was being used illegally, but they didn't ask for specific addresses or email forwards or any additional info, which seemed strange to me - you'd think they would want to find out who was abusing their system.
Anyway, it never stopped, I had to block the whole domain name, which of course still allowed me to receive them but they were just dumped into my deleted items file. Finally I just changed email addresses. I have no idea how it started and then snowballed into so many, several a day, of all kinds, ranging from get rich quick offers to life insurance to porn.