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DNS Block List.

A DNSBL is a list of DNS entries from which incoming emails should be blocked. It is also known as a DNS Black-hole List, or IP block list.

DNSBLs typically list open relays and servers which can be used for RNDR attacks. These are typically used as a means to reduce spam by blocking emails from known (or likely) spammers. However, it should be appreciated that DNSBL works on listing IP addresses and does not provide any intelligent filtering based on the content of an email.

DNSBL can be created and customised within a company, but there are also third party DNSBL services available on the internet.

DNSBL are sometimes also referred to as RBL or simply BL.

For more information see: