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Class C IP RBL blacklist not cool

Posted on Dec 5, 2009 by Paul White

Today I went through getting one of my new clients setup on the Feedback Loop with the major ISPs.  Most of the them came back saying I was approved to their feedback loop system, but one of them said I was not approved because I was found on an blacklist.

What is an RBL?

An RBL is short for Real Time Blacklist.  It is a database that tracks spam on the internet and what IPs are spamming whether it be email or comments.  RBL's use the DNS lookup system to quickly handle queries for the status about any given IP address.  SmarterMail is setup to use RBL's to help keep out the spam, and they are very effective with very few false positives.  However there are well over 100 RBLs each one with their own criteria.  There is a growing number of RBLs that block not based on your Class D IP address (, but instead they assume that if one IP is sending spam, then its neighbors are guilty as well.  So they block the Class C IP address ( 123.123.123.xxx)  This is also abreviated like so ( / 24 ) saying that the net mask should be applied to the first 24 bits, or the first 3 8 bit groups.  This would effectively blacklist everything from -

My situation

I currently have about 16 IPs pointing at my box one for each website with a few being shared.  I am very strict about spam.  I don't let it in, and i don't let it out.  However someone who moved into the datacenter, seems to think having your own server gives you the right to spam.  His IPs fall into my Class C block.  I have submitted a ticket to the datacenter to get this taken care of.  I understand that when you run a datacenter you can't always tell which customers will abuse the right to run your own server.  Fortunately I personally have met the guys who run the data center and I am sure they will get this taken care of quickly.

How to tell if I am on an RBL blacklist?

Goto MX Toolbox and type in your domain then click MX lookup
The ones that got me right now are

I understand the concept of Blacklisting by Class C IPs, but thats kind of like dropping a nuclear bomb in the middle of a neighborhood when you are just trying to kill the one house with terrorists.  Sure you will kill then, but you will also kill innocent people ( like me )

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