I was alerted by a colleague today that blackholes.us, which went out of business a couple of years ago, is now returning all IP addresses back as spam. To be fair, blackholes.us isn’t doing anything! It’s the company that now owns the IP block that used to be used for the blackholes.us RBL. More information can be found here.
So, if you are having mail blocked to some sites and you don’t know why! Ask them to check to see if they have this old RBL tucked away somewhere in their anti-spam and/or anti-virus solutions.
Happy emailing (if you can get through!).