Composite Blocking List

In computer networking, the Composite Blocking List (CBL) is a DNS-based Blackhole List of suspected E-mail spam sending computer infections.


The CBL takes its source data from very large spamtraps/mail infrastructures, and only lists IPs exhibiting characteristics such as:

The CBL attempts to avoid listing real mail servers, but certain misconfigurations of mail servers can make the system appear infected (for example, servers that send HELO with 'localhost' or a similar incorrect domain.)

Entries automatically expire after a period of time.

The CBL does not provide public access to gathered evidence.

CBL data are used in Spamhaus XBL list.

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