While we take very careful steps to insure our IP addresses are clean and not blocked by any provider, we can't guarantee that another company won't randomly block IP addresses they "consider" "bad". A normal procedure for a spam complaint is to notify the hosting company (firstname.lastname@example.org) of the issue and give them X hours to identify and correct the issue. When we receive these reports, we take immediate action to stop spam, then reply to the blacklist that the issue has been addressed. The next step, if we DONT reply, is to notify our datacenters. If we don't act by the time THEY notify us, we risk having our servers shutdown. We act - IMMEDIATELY. The last course of action by a blacklist should be a temporary server block. That'll get our attention (again) and everyone elses that's affected. By then, the offending customer is typically history because it'd be the 3rd notice from us.
There are occasions however that the IP address of a server MAY be blacklisted either incorrectly or because the blacklist provider did not provide ANY notice to us. If we get a notice, we act - fast!
With that said, there was an instance of a new server / ip assignment that was blocked by a few lists - before we even got the ip assignment. Once we learned of the issue, we contacted each blacklist as it was brought to our attenion and had the blocks removed. End of story.
So, if you are receiving a blacklist notification - that means we were never notified. Your first step is to contact the company you're sending mail TO ... if they won't do anything, then let us know and we'll deal with them. Please provide the full contact information along with the specific errors you're getting, in a helpdesk ticket. We'll address the issue during the normal course of business.