DNS is the public directory that connects your domain to websites, email, and other services. Business owners do not need to memorize every record type, but they should know what the common records control, who owns them, and why an unplanned change can affect customers. This glossary covers the DNS terms most likely to matter in day-to-day operations.
A and AAAA records
An A record points a hostname to an IPv4 address; an AAAA record points it to an IPv6 address. They commonly control where a website or subdomain loads. A wrong value can make a site unreachable, while a stale value can point visitors to an old host. Confirm the intended host and keep a copy of the previous value before changes.
CNAME record
A CNAME makes one hostname an alias for another hostname. It is often used for subdomains, hosted landing pages, verification endpoints, and email-provider tracking domains. A CNAME cannot coexist with certain other records at the same name, so follow the provider’s host-name instructions precisely rather than adding it at the root domain by assumption.
MX record
MX records tell other mail systems where to deliver inbound email for the domain. They point to mail-exchange hostnames and use priorities. During a mail-provider migration, an incomplete MX change can stop new messages from arriving even if website DNS still works. Record the current provider, MX hosts, and change owner before any migration.
TXT record
TXT records store text that other systems use for verification and policy. SPF, DKIM, DMARC, site-verification tokens, and TLS-RPT are commonly published as TXT records. Multiple TXT records can exist, but SPF and DMARC each need careful rules about their exact host and record count. A DNS dashboard splitting a long TXT value into quoted fragments is often normal.
SPF
SPF is a TXT policy that authorizes systems to send using an envelope-from domain. Publish one SPF policy, combine legitimate provider entries, and watch the ten-lookup limit. Learn the practical patterns in SPF record examples and test with a fresh message, not DNS appearance alone.
DKIM
DKIM uses a TXT record at a selector under _domainkey to publish a public key. The sending service holds the matching private key and signs messages. Each provider can use its own selector, so several DKIM records may be correct. See the DKIM record example for how the parts fit together.
DMARC
DMARC uses a TXT record at _dmarc to tell receivers how to handle messages that fail aligned SPF and DKIM. It can request reports and apply monitoring, quarantine, or reject policies. Do not publish duplicate DMARC records. Read the implementation checklist before enforcement.
Nameservers and TTL
Nameservers identify the DNS provider authoritative for a domain. Changing them moves control of the whole zone and can omit website, mail, or verification records if the new zone is incomplete. TTL is the caching time a resolver may use for a record; it explains why a correct new value may not appear everywhere immediately. It does not fix a malformed record.
Operational advice
Document the registrar, DNS provider, renewal contacts, record owner, and reason for every meaningful change. Give access only to people who need it, use MFA, and test website and email outcomes after changes. Run Beacon’s free domain check to review the public email-authentication records that depend on this DNS foundation.
Review DNS quarterly.