DNS lookup explained

What DNS lookup checks

A DNS lookup asks name servers for records attached to a domain. If a website does not load, email is not delivered, or a verification record is missing, DNS is usually one of the first systems to inspect. DNS changes can also take time to appear everywhere because resolvers cache results according to TTL values.

• A records point a domain to an IPv4 address.
• AAAA records point a domain to an IPv6 address.
• CNAME records alias one name to another hostname.
• MX records define which servers receive email.
• NS records show the authoritative name servers.
• TXT records often store SPF, DKIM, DMARC or service verification data.

When DNS lookup helps

Use DNS lookup when moving a domain to new hosting, confirming a CDN setup, debugging email delivery, checking whether a domain points to the right server, or verifying that a TXT record has been published. Comparing A and AAAA records also helps find cases where IPv4 works but IPv6 is misconfigured.

DNS troubleshooting checklist

When a domain does not work, check the authoritative name servers first. If the NS records point to the wrong provider, changing A or MX records elsewhere will not fix the live domain. Next, compare A and AAAA records. A domain can work on IPv4 while failing for IPv6 users if the AAAA record points to an old or unreachable server.

For email issues, inspect MX records and TXT records together. SPF, DKIM and DMARC records are commonly stored as TXT values and can affect whether messages are accepted, rejected or marked as spam. For website migrations, remember that DNS caching can delay visible changes even after the authoritative record is updated.

Examples of DNS problems

Website works for some users but not others: this can happen when cached DNS answers are different across resolvers. Some users may still see the old A record while others already resolve the new server.

Email sends but does not arrive: MX records may point to the wrong provider, or TXT records for SPF, DKIM and DMARC may be missing or malformed. DNS lookup helps verify the public records mail servers actually see.

Root domain works but www does not: the apex domain and www hostname are separate names. One may have an A record while the other needs a CNAME or its own A/AAAA records.

IPv6 users report failures: if an AAAA record exists but the server is not reachable over IPv6, some visitors may experience timeouts even while IPv4 users load the site normally.

FAQ

What is DNS propagation? It is the time needed for cached DNS answers around the internet to expire and refresh after a record changes.

Should a website have both A and AAAA records? Only if the server or CDN supports both IPv4 and IPv6 correctly.

Why do TXT records look messy? TXT records are flexible and are often used by many services for ownership verification and email security.

What is TTL? TTL is the cache lifetime for a DNS answer. Lower TTL values can make planned migrations easier, while higher values reduce repeated lookups.

Can DNS affect SEO? Indirectly, yes. DNS outages, broken redirects caused by wrong targets, or unreachable IPv6 records can affect crawling and user access.