I've watched and recorded Mozilla's spam performance for roughly 72 hours now, and as I thought, Friday was an unusually poor day for the Bayesian filters. I'll keep recording the numbers until a week has passed or until I forget and delete a batch of spam, whichever comes first, but for now here are the total stats for my mailbox over the last three days:
Total emails received: 102
Spam emails received: 81
Non-spam emails received: 21
Percentage of incoming email that is spam: 79.4%
Spam emails correctly identified by Mozilla: 69
Spam emails not identified by Mozilla: 12
Spam recognition rate: 85.1%
Non-spam emails incorrectly categorised as spam: 0
Considering that the anomalously bad day on Friday might have produced a lower-than-actual spam recognition rate figure, I think 85.1% is pretty respectable. But if I can keep doing this for a whole week, I'll probably get a figure very close to Mozilla's actual statistical success rate.
One thing I ought to point out is that Mozilla's algoriths are adaptive, and that with training they get better over time. A week after I'd started using the feature the success rate was much lower than it is now, and in three months time I'm sure it will be noticeably higher than it is today.
Another point I'd like to note is that since I've been running the spamfilter-enabled builds of Mozilla 1.3, seeing spam has actually been perversely enjoyable. If I see it, it's not been caught by the filter, so I get the satisfaction of categorising the mail as junk, thereby training the spam filters and improving them further. It's strange to say it, but I actually look forward to seeing spam now, because every spammer that gets an email past my filters is unwittingly improving my spam defences. That appeals to me.
When I post the final stats in a few days time, I'll also give information on where to get Mozilla Mail and how to use its spam filtering system. This really is a killer app for Mozilla, and just one of many areas where it kicks the equivalent Microsoft product (in this case, Outlook Express) all the way around the block without letting it touch the tarmac.