DNS (Domain Name System) is the internet's phonebook — it translates domain names into the addresses and configuration data that let browsers, mail servers, and other software find where to connect. Every time you visit a website, this lookup happens in the background, usually in under 50 milliseconds.
What happens during a lookup
- Your browser asks: what's the IP address for example.com?
- A recursive resolver — your ISP's, or a public one — checks whether it already has a cached answer.
- If not cached, the resolver asks the domain's authoritative name servers, which hold the actual record.
- The answer comes back and is cached for that record's TTL, so the next request skips the round trip entirely.
The record types that matter day to day
- A / AAAA — the IPv4 or IPv6 address a domain points to.
- CNAME — an alias mapping one domain name to another.
- MX — which mail servers handle email for the domain, and in what priority order.
- TXT — free-form text records, most commonly used for SPF, DKIM, and domain ownership verification.
Debugging "my email stopped working"
This is almost always an MX or TXT problem. Check that the MX record points to the correct mail provider, and that there's exactly one SPF-type TXT record — having two is treated as invalid by most receiving mail servers and can hurt deliverability more than having none at all.
Debugging "I changed my DNS and nothing happened"
This is TTL caching, not a broken change. Every DNS record has a Time To Live telling resolvers how long to keep the old answer cached before checking again. A record with a 24-hour TTL can take up to 24 hours to update everywhere, even though your DNS provider applied the change instantly. If you're planning a migration, lower the TTL a day or two in advance so the eventual cutover propagates fast.
Other things a lookup tells you
- NXDOMAIN or no records — the domain doesn't exist, isn't registered, or genuinely has no record of that type.
- CNAME conflicts — a CNAME must be the only record on that exact hostname; it can't coexist with an MX or TXT record on the same name.