A record vs AAAA record: what's the difference?

An A record maps a hostname to a 32-bit IPv4 address; an AAAA record maps the same hostname to a 128-bit IPv6 address. They are the same kind of DNS record — a direct address answer — for two different versions of the Internet Protocol. You publish an A record so IPv4 clients can reach your host, and an AAAA record so IPv6 clients can. Most production names carry both.

Quick Takeaways

An A record answers "what IPv4 address is this name?"; an AAAA record answers "what IPv6 address is this name?"
Both are address records that resolve in a single lookup — the only difference is the address family they return.
"AAAA" (quad-A) is four times the letters of "A" because an IPv6 address is 128 bits, four times the 32 bits of IPv4.
A resolver asks for whichever family the client needs: an IPv6-capable client requests AAAA first and falls back to A.
For email, a sending host that connects over IPv6 needs a matching AAAA and a reverse DNS (PTR) record, or Gmail and Yahoo may reject it.
You do not choose one instead of the other — publish both when your host has both an IPv4 and an IPv6 address.

| | A record | AAAA record | |---|---|---| | Points to | An IPv4 address (e.g. 203.0.113.10) | An IPv6 address (e.g. 2001:db8::1) | | Address size | 32-bit | 128-bit | | Protocol | IPv4 | IPv6 | | Resolves in | One lookup | One lookup | | Coexists at same name | Yes — with AAAA and other records | Yes — with A and other records | | Needed when | Any client still on IPv4 (nearly all) | Clients and mail servers reaching you over IPv6 |

What is an A record?

An A record ("address" record) maps a hostname to a single IPv4 address — the familiar dotted-quad numbers like 203.0.113.10. When a resolver looks up example.com and finds an A record, it has the final answer in one step and can open a connection. A records are the oldest and most common record type in DNS: almost every hostname on the internet has one, because IPv4 is still the default path for the vast majority of clients.

Because an A record returns an address directly, it is a valid answer at the zone apex (the bare root domain) and coexists with other record types at the same name. A single example.com can hold an A record, an MX record for mail, and TXT records for SPF and DMARC all at once.

What is an AAAA record?

An AAAA record — said "quad-A" — does exactly the same job as an A record, but for IPv6. It maps a hostname to a 128-bit IPv6 address, written as eight groups of hexadecimal separated by colons, like 2001:db8::1. We cover the format in depth in what is an AAAA DNS record.

The name is the clearest mnemonic for the difference. An IPv4 address is 32 bits; an IPv6 address is 128 bits — four times as large — so the record type gets four A's. IPv6 exists because the roughly 4.3 billion IPv4 addresses ran out; its vastly larger space (about 340 undecillion addresses) removes that ceiling. An AAAA record is how a name advertises its IPv6 address so that IPv6-capable clients can connect natively instead of falling back to IPv4.

A record vs AAAA record: what's the actual difference?

The only real difference is the address family each record returns. Everything else — how it is queried, that it resolves in one hop, that it can share a name with other records — is identical. Three practical points follow from that single distinction.

Address family. An A record returns an IPv4 address; an AAAA record returns an IPv6 address. A resolver does not "convert" between them — it asks specifically for the type the client needs.

Which one gets used. A dual-stack client (one with both IPv4 and IPv6 connectivity) typically requests the AAAA record first and prefers IPv6, falling back to the A record if no IPv6 route works. This behaviour, often called Happy Eyeballs, is why a host with a broken AAAA record can feel slow or unreachable for some users even though its A record is perfect.

Coexistence. A and AAAA are not mutually exclusive and never conflict. The standard practice for a public host is to publish both, so IPv4-only and IPv6-capable clients can each reach it. Unlike a CNAME, which cannot share a name with any other record, address records stack freely.

When do you need an AAAA record?

You need an AAAA record whenever a host has an IPv6 address that you want clients to reach over IPv6. In practice:

Public websites and services should publish both A and AAAA if their server or load balancer has IPv6 connectivity — it lets IPv6 users connect without translation and future-proofs the name.
You do not need AAAA if your host has no IPv6 address. Publishing an AAAA that points to an unreachable address is worse than having none, because dual-stack clients try IPv6 first and stall when it fails.
Keep A and AAAA in sync. If a host moves, update both records. A stale AAAA pointing at an old or dead address is a classic cause of "works for me, broken for them" reports.

If you only ever publish an A record, IPv6-only clients reach you through their provider's translation layer or not at all. As IPv6 adoption climbs, a matching AAAA increasingly matters for reachability and performance.

How do A and AAAA records affect email?

For mail, address records matter in two directions, and both are easy to overlook.

First, an MX record must point at a hostname that resolves via A or AAAA — never at a CNAME. When a sending server looks up your MX host, it needs a real address answer; an IPv6-capable sender will happily use your AAAA record to connect over IPv6 if one exists.

Second, and more consequential for deliverability: if your outbound mail server sends over IPv6, the major mailbox providers apply stricter rules. Both Gmail and Yahoo require an IPv6 sending host to have a valid reverse DNS (PTR) record whose name resolves back — via an A or AAAA record — to the sending IP, and to pass SPF or DKIM alignment. A mismatched or missing PTR on an IPv6 sender is a common reason otherwise-authenticated mail gets rejected. If you are not sure whether your sending IPs (v4 and v6) line up with their DNS, Palisade's Email Security Score checks the records that mailbox providers actually look at before deliverability suffers.

Common issues with A and AAAA records

A few failure modes come up again and again.

A stale or wrong AAAA record. The most painful one: a host has a broken IPv6 path but still advertises an AAAA. Dual-stack clients try IPv6 first, time out, and only then fall back — so the site loads slowly or intermittently for a subset of users while looking fine to everyone else. Fix the IPv6 route or remove the AAAA.

Publishing AAAA for a host with no IPv6. If your server genuinely has no IPv6 address, do not invent an AAAA record. An address record must point at a reachable address.

Forgetting to update one of the pair. When you renumber a host, update both the A and the AAAA. Editing only one leaves half your users pointed at a dead address.

Confusing AAAA with a different record type. AAAA is strictly IPv6 addressing. It is unrelated to MX, TXT, or PTR records, even though those can all live at related names.

Frequently asked questions

Is an AAAA record just a bigger A record?

Functionally, yes — same job, different address family. An A record carries a 32-bit IPv4 address and an AAAA record carries a 128-bit IPv6 address. The resolution process is otherwise identical.

Do I need both an A and an AAAA record?

Publish both when your host has both an IPv4 and an IPv6 address — that lets every client reach you natively. Publish only an A record if the host has no working IPv6 address; a broken AAAA is worse than none.

Which record does a browser use if both exist?

A dual-stack client generally requests the AAAA record first and prefers IPv6, falling back to the A record if the IPv6 connection fails. That is why a broken AAAA can degrade the experience even when the A record is correct.

Does IPv6 affect whether my email gets delivered?

It can. If your mail server sends over IPv6, Gmail and Yahoo require a valid reverse DNS (PTR) record for that IPv6 address plus passing authentication, or they may reject the message. Sending over IPv4 with correct records avoids that specific pitfall.