A few months ago, I took on managing a couple other email domains for one of my personal clients. Since then, I've seen our SPAM levels rise. I have spent a little time tweaking spam restrictions for my domains off and on for a while, but recently I have started really cracking down.
If you are using SmarterMail, one thing you can do is add in content filtering. I've added in a domain wide filter based on domain names that, in my opinion, are spammers. The thing I love most about setting up the filter is that I can have the mail server send a bounce message back. I like this approach, because it should reduce the amount of this crap we get over time. That said, I've noticed that a number of these a-holes have a multiple domains and proceed to blindly send in a cycle day after day.
All that said, I'm compiling a list of suspected spam domains, and intend to make a file available with these for anyone that would like to use them. I've only been gathering these for about a week now, but here's my current list of offending domains: