Re Dave's Spam Stuff, people disagreeing with Dave seem to forget that there is also another negative effect. If your ISP uses a silly blocking procedure, you likely won't see my (or Dave's) email.
Sometimes I am at loss, sometimes you are. If you feel you might be at loss, advise your ISP (where did we hear this before?) to switch to something like greylisting, which catches more spam than any other mechanism I've seen (from experience and practice), yet doesn't block any single legitimate mail.
So, the tactics is that if enough users complain they can't receive mails directed at them and they really want them (like mails from me: everybody wants one of those! :), ISP will be forced to fix their improper blocking ;)