Black List check
I honestly think I spend more time tinkering with spam filters than I do in just deleting spam manually. I have a very public email address displayed prominently on my site and I've had the same email address for over 15 years. I get a lot of spam, but most of it I get rid of with very simple regex filters. I tried fancy Beysian filters and spamassasin. They were all more trouble than they were worth and they take up A LOT of CPU! The most annoying part of so-called smart spam filters is that they get way too many false positives. My own custom filters do get false positives, but rarely. I focus on getting rid of the easy to detect spam. After all that I still end up with maybe a 50/50 ratio of good mail to spam, but that's low enough that I don't waste much time during the day pressing the delete button.
SURBL - Spam URI Realtime Blocklists
Use the following tool to check if an IP or domain name is in a URIBL: