DNSBL (RBL) Comparison
In an attempt to find a good, low false positive RBL, I analysed my mail server logs writing a couple of scripts. I have put up this page so that other mail server administrators have some figures before them while choosing their list of RBLs.
I do not advise use of more than three (remote) RBLs since it usually involves serious performance penalty.
Methodology
Testing was done for minimum of 10 days of each month. Each day a cron job parsed my qmail-smtpd log files and got a list of unique IPs, which were checked by a perl script against the said RBLs. As a side effect of the exercise, I also checked whether the IPs had their reverse dns (rdns) set up since I gather from experience that refusing to accept mails from IPs having no rdns blocks a huge number of spam.
Note: I recommend you all to have a look at UCEPROTECT-Blacklists. Their false positive rate is not very high, their technical support is responsive but their main USP for me is that they allow their zone files to be downloaded free of charge unlike other RBLS like Spamhaus or Spamcop.
For ease of comparison, figures given below are expressed as percentage of total unique IPs.
| Time Frame | zen.spamhaus.org | dnsbl-1.uceprotect.net | bl.spamcop.net | b.barracudacentral.org | dyna.spamrats.com | Missing RDNS |
| Mar 09 | 81.4 | 62.8 | 67.3 | 80.3 | -- | 33.8 |
| Apr 09 | 90.1 | 72.2 | 75.2 | 88.5 | 42.6 | 34.2 |
| May 09 | 90.2 | 72.7 | 75.2 | 88.9 | 43.8 | 32.6 |
| Jun 09 | 90.3 | 73.4 | 75.4 | 87.6 | 37.0 | 34.9 |
| Jul 09 | 93.3 | 77.9 | 81.4 | 89.5 | 38.7 | 39.8 |
| Aug 09 | 92.6 | 81.1 | 82.1 | 92.3 | 39.0 | 39.7 |
| Sep 09 | 94.1 | 73.2 | 72.1 | 94.2 | 43.3 | 27.2 |
| Oct 09 | 95.6 | 79.4 | 74.4 | 95.3 | 38.1 | 27.9 |
| Dec 09 | 89.9 | 82.3 | 60.4 | 90.1 | 37.3 | 26.1 |
| Jan 10 | 85.4 | 81.1 | 50.3 | 78.9 | 32.3 | 20.5 |