Glossary
CNAME record
A CNAME (canonical name) record is a DNS record that makes one hostname an alias of another. Lookups for the alias follow it to the target name, so the alias always resolves to wherever the target points.
What Is CNAME Record?
In short A CNAME looks like track.example.com CNAME tracking.vendor.com.
A resolver asking for track.example.com is told to ask for tracking.vendor.com instead and returns that name's addresses. The vendor can move its servers without you changing your DNS.
A name that has a CNAME can't hold any other record (RFC 1034, restated more firmly in RFC 2181). So you can't put a CNAME on the root of your domain, where the NS, SOA and MX records live, and MX and NS records must point to real hostnames, never to a CNAME.
CNAME Record Example
Example: a cold email team adds go.example.com as a CNAME to its sending tool's tracking host. Links in its emails now start with go.example.com, so its click tracking no longer shares a domain with thousands of other senders.
CNAME Record in Practice
Email uses CNAMEs in two places. A custom tracking domain is a subdomain of yours pointed by CNAME at your sending tool's tracking server, so links and open pixels use your domain instead of one shared by every customer of the tool. DKIM delegation uses CNAMEs too: Microsoft 365, for example, asks you to publish selector1._domainkey and selector2._domainkey as CNAMEs so it can host and rotate your keys.
FAQ
What is a CNAME record?
A DNS record that makes one name an alias of another, for example track.example.com pointing to tracking.vendor.com. Anyone looking up the alias gets the target's addresses.
What is the difference between a CNAME and an A record?
An A record maps a name to an IPv4 address. A CNAME maps a name to another name, which then resolves to an address. Use a CNAME when someone else controls the target and may change its IPs.
Can a CNAME exist alongside other records?
No. If a name has a CNAME, it can't hold MX, TXT or any other ordinary record (RFC 1034 and RFC 2181). That is why you can't put a CNAME on your root domain.
What is a custom tracking domain?
A subdomain of yours, such as track.example.com, set as a CNAME to your sending tool's tracking server. Links and open pixels then use your domain instead of a domain shared by every customer of the tool.
Why does Microsoft 365 use CNAME records for DKIM?
So Microsoft can host and rotate your DKIM keys. You publish selector1._domainkey and selector2._domainkey as CNAMEs that point to keys Microsoft manages.
Do This in Ken
Do This in Ken
Delivery handles DNS setup for the sending domains it provisions, so you don't add CNAME, MX or TXT records by hand.
- Module
- Delivery
- Open in Ken
- /features
The new Ken opens to the waiting list in batches.
Related
- GTM Glossary
Every GTM term, grouped by topic.
- MX record
- DKIM (DomainKeys Identified Mail)
- SPF (Sender Policy Framework)
- PTR record
- Sender reputation
- Ken
Sources
| Source | Checked |
|---|---|
| RFC 1034: Domain Names, Concepts and Facilities | |
| RFC 2181: Clarifications to the DNS Specification | |
| Microsoft Learn: How to use DKIM for email in your custom domain |
Changelog
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