DNS
The Domain Name System: the distributed database that turns domain names into IP addresses and holds the records mail depends on, such as MX, TXT and PTR.
What it means
DNS is a hierarchy of zones, each served by authoritative nameservers, from the root through top-level domains like com down to individual domains. Resolvers look names up on behalf of applications and cache the answers for as long as each record's TTL allows. The design is in RFC 1034 and RFC 1035 (1987).
Email relies on DNS at every step. A sending server finds where to deliver through MX records, and receivers check SPF, DKIM, DMARC, MTA-STS and BIMI through TXT records, reverse DNS through PTR records, and blocklists through DNS queries. A DNS outage or misconfiguration therefore shows up as mail problems: temporary errors, authentication failures or delivery to the wrong place.
DNSSEC adds signatures that let resolvers verify answers.
Related terms
On this site
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- RFC 1034: Domain Names: Concepts and Facilitiesrfc-editor.org
- RFC 1035: Domain Names: Implementation and Specificationrfc-editor.org
- RFC 9499: DNS Terminologyrfc-editor.org
All 432 terms in the glossaryThe wiki: blocklists and bounce codes