As an e-mail provider with over 10 million mailboxes...........that's not 100% accurate. But anyhow.Email providers resort to blacklisting rather than more sophisticated spam detection solutions, because it's cheap and dirty, keeps their customers happy with less perceived spam, and saves the provider money while keeping their customers ignorant of the fact that legitimate email sent to them is potentially blocked.
Good news - at the moment you're not listed on any of the major blacklists. Either you've managed to get de-listed, or your issue wasn't RBLs (properly-implemented RBL rejections will show up as 571 messages in your mail log).
Something you should address immediately: add txt records in your DNS for SPF. Last I looked, Microsoft relied fairly heavily on SPF at its content filter stage. I don't know if they back-feed their content filter stuff into private RBLs or now.
Wes
Bookmarks