# What is a CNAME record? DNS Alias Records Explained > What a CNAME record is, how DNS aliases resolve to a canonical name, the rules that trip people up (no apex, no siblings), and how CNAMEs power email setup. ## What is a CNAME record? A CNAME (Canonical Name) record is a [DNS](/learning/what-is-a-dns) record that makes one hostname an alias for another. Instead of holding an address of its own, the alias points at a canonical name, and the resolver follows the pointer to whatever records that name holds — its A record, [MX record](/learning/what-is-an-mx-record), and so on. It is the DNS equivalent of a mail-forwarding order: query the alias, and you are redirected to the real destination. CNAMEs exist to save you from maintaining the same address in several places. Point `mail.yourdomain.com` at your provider's hostname once, and if that provider changes the underlying IP address, your alias follows automatically — you never touch your own zone. ## How does a CNAME record work? A CNAME record stores an alias and its target. When a resolver looks up the alias, it does not get a final answer; it gets the canonical name and repeats the lookup against *that*. For example, a CNAME mapping `mail.yourdomain.com` to `ghs.googlehosted.com` sends anything addressed to `mail.yourdomain.com` on to Google's servers, which supply the actual IP address. The chain can be more than one hop deep — an alias can point to another alias — but every extra hop adds a lookup and a point of failure, so keep chains short. ![CNAME record examples](/images/figures/what-is-a-cname-record-examples.webp) This is why CNAMEs are everywhere in email setup. Providers like Google Workspace and many marketing platforms ask you to publish CNAME records so their [DKIM](/learning/what-is-dkim) keys and tracking hostnames resolve through your domain while they manage the underlying values. You publish the alias once; they rotate the target behind it. ## The rules that trip people up CNAMEs behave differently from most records, and three constraints cause nearly every misconfiguration: - **A CNAME cannot share a name with any other record.** [RFC 1912](https://datatracker.ietf.org/doc/html/rfc1912) states that a name with a CNAME record may have no other data. If `mail.yourdomain.com` has a CNAME, it cannot also carry an [MX](/learning/what-is-an-mx-record) or [TXT](/learning/what-is-a-txt-record) record — the alias replaces them all. Trying to add a sibling record is the most common CNAME error. - **No CNAME at the zone apex.** The root of your domain (`yourdomain.com` with no host in front) must hold SOA and NS records, and the no-siblings rule means it cannot also be a CNAME. Use an A record — or a provider's "ALIAS"/"ANAME"/"CNAME flattening" feature, which returns an address at the apex while behaving like an alias. - **An [MX](/learning/what-is-an-mx-record) target must not be a CNAME.** RFC 5321 requires a mail server hostname to resolve to an address record directly. Pointing an MX at a CNAME is undefined behaviour that some receivers reject. ## CNAME vs. other DNS records It helps to place the CNAME next to its neighbours: - An **A record** maps a name straight to an IPv4 address; a CNAME maps a name to *another name*. - A **TXT record** holds free-form text such as SPF or DKIM values; a CNAME holds a single canonical hostname. - An **MX record** routes mail and must point at a real hostname, never an alias. CNAMEs also underpin authentication and branding: some [SPF](/learning/what-is-spf), DKIM, and [BIMI](/learning/what-is-bimi) delegations are published as CNAMEs so a provider can maintain the record for you, and the authentication result still surfaces in the message's [email header](/learning/what-is-an-email-header). ## Why CNAME records matter - **One place to update.** Change the canonical name's address and every alias follows, instead of editing each record by hand. - **Cleaner provider onboarding.** Third-party mail and marketing services hand you CNAMEs so they can rotate keys and endpoints without asking you to touch DNS again. - **Fewer stale records.** Aliasing to a vendor-managed hostname means you are never left publishing an IP address the vendor has already retired. Check what a name currently resolves to — and whether a CNAME is pointing where you expect — with the [DNS lookup tool](/tools/dns-lookup), and confirm your signing hostnames with the [DKIM lookup](/tools/dkim). ## Frequently asked questions ### How long does a CNAME change take to take effect? There is no fixed 48-hour rule. Propagation is governed by the record's TTL: resolvers that cached the old value keep serving it until their copy expires, which with a short TTL is only minutes. Lower the TTL a day before a planned change, then raise it again once the new value is live. ### Why can't I add a CNAME on my root domain? Because the apex already carries the mandatory SOA and NS records, and a CNAME is not allowed to coexist with other records at the same name. Use an A record at the apex, or your DNS provider's flattening feature (ALIAS/ANAME) if you need alias-like behaviour there. ### Can a CNAME point to another CNAME? Yes, chains are legal, but each hop is another lookup and another dependency. Keep chains to a single hop where you can; long chains slow resolution and multiply the ways a change can break. ### Does a CNAME affect email authentication? Only indirectly. Many providers publish DKIM and other authentication data as CNAMEs so they can manage the values for you. The alias itself is neutral — but if it points at the wrong target, the authentication lookup fails, so verify it resolves correctly. ### What's the difference between a CNAME and a URL redirect? A CNAME operates in DNS and redirects *name resolution* for every protocol at that hostname. A URL redirect happens at the web-server or HTTP layer and only affects browser traffic. They solve different problems and are not interchangeable. ## Related reading - [What is a DNS?](/learning/what-is-a-dns) - [What is an MX record?](/learning/what-is-an-mx-record) - [What is a TXT record?](/learning/what-is-a-txt-record)