Noah Lorang at 37signals writes about how they send emails with a high acceptance rate:
Mail delivery is more of an art than a science. We’ve found that even when you “play by the rules”, there’s still times when a major provider will reject all your mail without notice. Usually it takes a couple emails to to the providers abuse address, and things get resolved. In spite of these “out of our control” issues, we’ve found a few things help us keep delivery rates up.