Glossary definition

DNS blacklist (DNSBL)

A DNSBL is a blocklist published over DNS: querying a specially formed name reveals whether an IP or domain is currently listed by that operator.

How GTM Inboxes uses this term

GTM checks sending IPs against DNSBL operators on an adaptive schedule, raises alerts on listings, and can rotate a blacklisted IP through an approval-gated recovery executor while the listed address is retired.

How a DNSBL query works

The client reverses the IP octets, appends the list's zone, and issues a DNS query. An answer means listed and the returned code often encodes a reason; no answer means not listed on that list at that moment.

What a listing does and does not mean

Blocklists differ widely in impact. A listing is a reputation signal for that list's users, not a universal verdict on your mail. Prioritize lists that major receivers actually consult, and pair delisting with a fix for the behavior that caused the report.

Related glossary terms

Shared vs dedicated SMTP IP

A shared SMTP IP carries traffic from many senders, while a dedicated SMTP IP carries traffic that a single workspace controls and is accountable for.

SMTP recovery event

An SMTP recovery event records that a sending resource failed, what containment applied, and where the fix stands, so recovery is a tracked workflow instead of ad hoc firefighting.

Domain age

Domain age measures how long a domain has existed since registration, which readiness reviews use as a conservative risk signal for cold email launch timing.

Related workflows

Check blacklist status

Query common DNSBL operators for an IP or domain.

Check a real domain

Move from the definition to a practical DNS and authentication check.

Seed placement workflow

How the concept shows up in the pre-launch evidence workflow.

Browse the glossary

Every cold email infrastructure term GTM models, checks, or gates.

Next step

See how listings fit into a structured deliverability incident response.

Read the incident triage workflow