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

DNS is the distributed directory of the Internet. It contains more than a website address: it also describes email routing, aliases and many forms of domain-control verification. Understanding five record types covers most common configurations.

What is a DNS zone used for?

When you enter a domain name, a resolver queries DNS for the appropriate information. The answer depends on the type requested. A browser usually searches for an A or AAAA address; a mail server searches for MX records; A service may query a TXT record to verify a policy.

The data is cached for a duration defined by the TTL. A correction can therefore be correct on the authoritative server without being immediately visible everywhere.

A and AAAA: service addresses

An A record associates a name with an IPv4 address. An AAAA record performs the same role for IPv6. One domain may publish both in order to be accessible on both protocols.

example.fr.      A     192.0.2.10
example.fr.      AAAA  2001:db8::10

Publishing an AAAA record implies that the service actually works in IPv6. An old IPv6 address can cause a breakdown only for some visitors, which makes it more difficult to spot.

CNAME: assign another name to a target

A CNAME indicates that a name is an alias of another name. It is convenient to point www.example.fr to a target managed elsewhere without copying its address.

www.example.fr.  CNAME  site.hebergeur.example.

A CNAME should not usually coexist with other records on the same name. At the root of the domain, some providers offer equivalent mechanisms called ALIAS or ANAME, which are not universal standard DNS types.

MX: where to deliver emails

MX records refer to servers that receive domain messages. The number placed before the server is a priority: the lowest value is tried first.

example.fr.  MX  10 mail1.example.net.
example.fr.  MX  20 mail2.example.net.

The target of an MX must be a server name, not an IP address. Deleting or modifying an MX record without preparing the destination service can interrupt email delivery.

TXT: policies and evidence of control

TXT records contain text interpreted by other services. It is used in particular for SPF, DMARC, validation of a domain or certain signatures. Two TXT records may be used for different uses, but some policies impose a single logical value.

For example, publishing two separate SPF policies for the same name usually invalidates SPF. Combine all authorized sending sources into a single policy.

TTL: How long do you keep the answer?

TTL is expressed in seconds. A short value speeds up propagation during a migration but increases the number of queries. A long value reduces queries while keeping stale data visible for longer.

Before a planned migration, lower the TTL early enough. After stabilization, raise it to a suitable value. The TTL does not guarantee that all intermediaries will abandon their cache at exactly the same time.

Frequent errors

• leave an A or AAAA record pointing to an old server;
• use a CNAME where other data must coexist;
• indicate an IP address directly as an MX target;
• publish multiple conflicting SPF policies;
• modify a zone without recording the previous values and TTL.

To prepare an online release, complete this reading with the guide DNS audit before production.

To determine the order of intervention when a check fails, see also how to prioritize a domain alert.

Published on 5 August 2026.