Comment by marcoamorales

I wouldn't say that Rackspace intentionally submits their IP blocks for DNS blacklisting. Consider that on Rackspace's cloud you can build a cloud server and you will get a 'recycled' IP from their block. This IP could had been used by other people for other purposes. You never know who could've used your IP for what purposes. Having those blocks blacklisted makes sense when you think of that.