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These reports show the lookup results for the DNSBLs used by our mail hosts to screen incoming port 25 mail connections. For a similar more comprehensive comparison of all public DNSBLs, see Jeff Makey's Blacklists Compared pages.

Source Data

The IP addresses used for lookup are the set of addresses that have successfully connected to port 25 on our mail hosts or spam traps in the week ending at midnight each Saturday.

It should be noted that a permanent IP entry is NOT made in the SpamCannibal zone file if the IP address is found in one of the DNSBLs used by the mail host. Thus, the survey results for SpamCannibal represent IP addresses that were not found elsewhere at the time of initial lookup

Our mail hosts run the SpamCannibal daemon. The SpamCannibal database maintains a semi-permanent cache of IP's which have a positive DNSBL lookup outcome. SpamCannibal also maintains a permanent record of locally detected spam sources for export in its zone file. Once a host IP is recognized as a spam source one way or the other, it can never again connect at the TCPIP transport layer and will not again appear in the set of connecting IP addresses used for these comparisons. .

In simple terms, the dataset used each week for these charts consists of all NEW IP's every week except for those host IP's from which valid email is routinely received. To put this in perspective, we receive at most a few hundred valid emails a day, mostly from large ISP's. An estimate of the number of non-spam, repeating IP's in the data set is probably under a hundred.

Methodology

The comparison and report generation is done using the Perl module Net::DNSBL::Statistics which provides a script that accepts one or more lists of IP addresses and can perform the DNSBL interrogations in parallel. In addition, it perform checks for missing PTR records and detects matches to GENERIC reverse host name patterns.