I know this isn't the answer people are looking for, but I implemented a set of rules on our firewall to block countries that my users shouldn't have any business talking to. I did this more for content filtering but I noticed our spam decreased drastically when I did that. I am talking we went from probly around 1,000 spam a day to about 20. The downside is sometimes your users do have a legit reason to talk to IPs in these countries so you have to unblock them one at a time, but imo it was worth it. I use zen.spamhaus.org as an rbl, which helps filter the U.S. spam we get. I work for a school district though here in the U.S. so 90% of our emails we get are from parents here in our town or other school districts here in our state. I know businesses email people in other countries all the time, so you have to think about it a lot before you would do something like this. Between the firewall rules, spamhaus, and the anti-spam system zimbra has, we don't have any problem at all with spam as of now (knock on wood). We get a few here and there, but it isn't a problem. Our users realize that spammers dedicate much more time getting spam into our inboxes than I have to keep them out, so one every now and then isn't too shabby.  |