I added a simple little widget in the right column of the front page to list the percentage of my email that was spam yesterday and the long-term average percentage of spam I’ve been receiving.
The definition of "spam" here is simple: it’s what SpamAssassin tags as spam. That means the count will include some false positives, and it’ll miss a few pieces of spam. But my experience with my configuration suggests that these numbers largely cancel each other out. I think it’s close enough for my purposes.
There are a couple of other factors here that may make the spam percentage lower than it otherwise would be. I have a large list of blacklisted domain names and netblocks in my Sendmail configuration. I’m not using anything like MAPS RBL here. I’ve just constructed a list based on where a lot of my spam seems to come from. It’s been pretty effective for me (it’s currently blocking an average of 20,000 spam messages a month). It’s hard to say how many of those messages would truly have gotten through to me; some of them are sure to be dictionary attacks or otherwise sent to invalid addresses. But I have no doubt that my spam percentages would be significantly higher without the blacklists there.
Also, I’ve used temporary autogenerated addresses for a lot of things like posting on Usenet. And my main web page currently has uniquely-generated email addresses on each page. Those are real addresses mail sent to them will get through to me. But their nature makes it very easy for me to disable any that I find to have been harvested by spammers. While I’m not currently taking advantage of it, I do also have the capability to make those addresses work only for a short period of time. If the spam flood from them becomes too much of an nuisance, I may turn that on. It seems unlikely to seriously inconvenience legitimate users and if the time window were small enough, it would make the addresses useless for spammers.
I added some information on my blacklist blocking to the spam stats box on the main page. Some of the blacklist information is discussed above. Since I wrote that, I’ve started using the Spamhaus SBL blacklist. At the time of this writing, it accounts for a very small percentage of my overall blacklist blocked messages.