What are the most important DNS records?

For a working site and email: A/AAAA (where the site lives), MX (where email is received), NS (who controls the zone), and TXT (SPF/DKIM/DMARC for email authentication). CNAMEs alias names to others.

Why did my site go down after a DNS change?

A wrong A/AAAA record, a deleted MX, or reset NS records will break resolution, and changes propagate on a TTL delay so the impact can appear minutes later and spread as caches expire. Checking the live records confirms what is actually published.

The slow accumulation of stale or wrong DNS records — leftover campaign entries, an old mail provider's MX, a dangling CNAME pointing at a dead service. It does not error; it degrades reliability and can open subdomain-takeover risks.

DNS records explained: A, AAAA, CNAME, MX, TXT and NS

DNS is the address book of the internet: it turns your domain into the numbers and destinations that browsers and mail servers actually use. A single wrong record can take a site or its email offline instantly. Here is what each common record type does — and how to catch a bad edit.

The record types you actually deal with

A record — points a domain to an IPv4 address (the server hosting your site). Wrong A record = site unreachable or pointing at the wrong server.
AAAA record — the same, for an IPv6 address.
CNAME record — an alias that points one name at another name (e.g. www → yourdomain.com, or a subdomain at a SaaS host). Cannot coexist with other records on the same name.
MX record — mail exchanger: which servers receive email for the domain, with priorities. Wrong MX = email stops arriving.
TXT record — free-form text used for verification and email auth (SPF, DKIM, DMARC all live in TXT). A broken TXT quietly breaks deliverability.
NS record — the authoritative name servers for the domain. Change these and you hand control of all the above to a different DNS provider.

How DNS breaks a site or email

DNS problems are unusually damaging because they are invisible until something stops resolving, and because changes propagate on a TTL (time-to-live) delay — so a bad edit can look fine for minutes and then break widely as caches expire.

The classic incidents: someone repoints an A record during a migration and forgets a subdomain; an MX record is deleted and inbound mail bounces for hours; a registrar transfer resets the NS records and the whole zone reverts to defaults; or a TTL is set so long that a fix takes a day to take effect.

DNS drift: the slow, silent failure

Beyond outright breakage, DNS "drifts" — records get added for a campaign and never removed, an old mail provider's MX lingers, a dangling CNAME points at a decommissioned service (a subdomain-takeover risk). None of this errors; it just accumulates until it bites.

You can inspect any domain's live A, AAAA, MX, NS and TXT records with the free DNS record checker.

Catching bad DNS changes

The defence is to watch the records that matter and get told when they change unexpectedly. VigilDog's DNS monitoring tracks your DNS and email records across every domain you manage and flags drift — so a mistaken edit or a dropped MX is a notification, not a support ticket from a client.

Frequently asked

What are the most important DNS records?: For a working site and email: A/AAAA (where the site lives), MX (where email is received), NS (who controls the zone), and TXT (SPF/DKIM/DMARC for email authentication). CNAMEs alias names to others.
Why did my site go down after a DNS change?: A wrong A/AAAA record, a deleted MX, or reset NS records will break resolution, and changes propagate on a TTL delay so the impact can appear minutes later and spread as caches expire. Checking the live records confirms what is actually published.
What is DNS drift?: The slow accumulation of stale or wrong DNS records — leftover campaign entries, an old mail provider's MX, a dangling CNAME pointing at a dead service. It does not error; it degrades reliability and can open subdomain-takeover risks.