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DNS, the Domain Name System, is the distributed directory service that makes the internet usable by humans. It translates memorable domain names like example.com into the numeric IP addresses that computers need to connect, and it stores many other kinds of records that direct email, verify ownership, and route traffic.
A DNS lookup walks a hierarchy: a resolver queries a root server, which points to the top-level domain servers for endings like .com, which in turn point to the authoritative name servers for the specific domain. Those authoritative servers hold the actual records, and results are cached along the way according to each record's TTL.
DNS holds many record types, each with a purpose. A and AAAA records map names to IPv4 and IPv6 addresses; MX records direct email; TXT records carry SPF, DKIM, and DMARC data plus domain verification tokens; CNAME records alias one name to another; and NS records delegate authority for a zone.
For email and deliverability work, DNS is foundational. Verifying MX records confirms a domain can receive mail, TXT records reveal authentication setup, and A records support fallback delivery. A single DNS lookup tool can inspect all of these, making DNS the first place to look when diagnosing delivery or configuration problems.