At work we have been using DNS Black Lists for a long time to deny spam coming into our email systems. There are a number of places you can check to see if you are on one of these lists but I figured I would write my own web 2.0 version. So here it is my own DNSBL checker. I believe it has most of the major lists on it but if I find more I'll add them. I'm also going to try to post more about how it is all put together.