After upgrading our defenses against spam, I'm amazed to see how well Spamhaus ZEN works. Their Effective Spam Filtering paper shows a pie chart with a benchmark of 75% blocked by Spamhaus ZEN. As you can see from the very-purple pie chart, below, we're getting even better results here. There isn't much left for SpamAssassin to look at, which is good news (server resource-wise).
All the "purple" and "red" spam, below, is turned away at the RCPT TO stage. The rest is accepted, with the spam filed in a "Blocked" folder to check for false positives, train Bayes, etc. I'm hoping that as Bayes trains up the percentage of "green" will go down even further, but even at this point, the number of false negatives is very manageable.
| Count | Avg/hr. | Percent | |
|---|---|---|---|
| Spamhaus ZEN | 1375 | 19.1 | 83.9% |
| SpamAssassin >15 | 66 | 0.9 | 4.0% |
| SA URIDNSBL | 26 | 0.4 | 1.6% |
| SpamAssassin <15 | 10 | 0.1 | 0.6% |
| Non-spam | 162 | 2.2 | 9.9% |
| TOTAL | 1639 | 22.8 | 100.0% |
