One of my companies sends hundreds of thousands of emails a month from Rackspace servers. What can you tell me about this ? What blacklists, where ? We don't

One of my companies sends hundreds of thousands of emails a month from Rackspace servers. What can you tell me about this ? What blacklists, where ? We don't show up on any of the easily checkable ones. We are of course CANSPAM compliant, use good email headers, unsub etc. etc.