When you receive this error, it means that the IP address you’re attempting to send email from has been blocked by Spamhaus. In addition to the anti-virus and anti-spam software, we are relying on services provided by reputable organizations who maintain various RBLs to help stop spam e-mail from entering our systems. Generally RBLs are lists of sources that are known to generate spams. Before our servers accept SMTP connections from an IP, they consult these RBLs to see if that source is listed. If it is, the connections are rejected and the sender receives a message with a concise reason as to why. Normally this is in a form of a URL that the sender can click on to find out more detail.
RBLs Currently in Use
After considerable research and testing, we have chosen to use Spamhaus. Our abuse department has been working with these organizations over the years and have found them to be responsible and responsive. Therefore we are confident that the chances are very low that they falsely add innocent hosts to their lists.
Getting Your IP(s) Delisted
As mentioned, if you discovered that someone trying to send you E-mail but could not, or you are sending E-mail and are getting bounced messages indicating the source is listed by one of these RBLs, it means that there is really a problem with that source. A problem can range from the source being an open-relay which allows anyone (spammers) to use it to disseminate spam or the source host is compromised again allowing viruses and spam to originate from there. Please follow the link included in the bounced message to find out more detail about the nature of the blockage. Often, there are also information on how to take corrective actions and fix the problem as well as information on how to remove that source IP from these lists. Please do your part and help us put a damper on the rampant spam problem.
While you wait for your IP to be delisted, or work with your ISP to resolve this issue, you can always use Webmail (http://mail.yourdomain.com) to send email.