Deliverability
DNSBL
DNS-based Blackhole List. A blacklist queryable via DNS to check if an IP is flagged for spam.
Definition
DNSBL (DNS-based Blackhole List) is a blacklist that can be queried using the DNS protocol. When an email server receives a message, it can quickly check if the sending IP is listed on a DNSBL by performing a DNS lookup. This makes blacklist checks very fast and efficient. Major DNSBLs include Spamhaus, Barracuda, and SURBL.
Examples
Query: 4.3.2.1.zen.spamhaus.org → Response indicates if 1.2.3.4 is listed
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