"She who shares my hookup" gets virtually zero such mail on her MSN account. It may be partly because the email addy looks obviously like a business.
My hotmail account was getting about 80 such messages a day, but in recent months it's been cut to about a dozen per week. They DO filter and block a lot of it, but there's the inevitable bit that gets through. They do a pretty good job of dumping it all into Bulk Mail, although I've had my newsletter from one of my State Representatives dumped down there recently. ... maybe that means something ??????
You can of course block individual senders, or individual ISPs if you want, although there's a limit on how many addys you can put in your block list. My experience with trying to do it that way was that the real offenders get new addys faster than you can block them.
MSN, and probably many other email services, offers "premium" services that claim that you get better filtering if you pay more; but I'm dubious that the better filtering would compensate for all the other "service enhancements" they try to include in such subscriptions; and I have no reliable info on whether the filtering is actually better.