What is a CNAME (Canonical Name) record?
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Your ESP just handed you a CNAME record to add to your DNS, and now you're staring at your domain registrar wondering what on earth it actually does. Fair question.
A CNAME (Canonical Name) record is a DNS alias. It points one hostname to another hostname, so that when someone's mail server (or browser) looks up the first name, DNS quietly redirects that lookup to the second name and follows it from there.
A concrete example makes this easier to picture. Say your domain is tidalmail.com and your ESP wants you to set up a custom tracking subdomain. You'd add a record like this:
tracking.tidalmail.com CNAME links.esp-provider.com
Now, anything looking up tracking.tidalmail.com gets redirected to links.esp-provider.com. Your ESP controls that destination, so when they update their servers, your tracking subdomain follows along automatically. You don't have to touch your DNS again.
That's the key reason ESPs ask for a CNAME rather than an A record. An A record points to a fixed IP address. If your ESP ever changes their infrastructure, your A record would break and you'd have to update it manually. A CNAME follows the destination wherever it moves.
In email specifically, you'll run into CNAME records most often in three situations. First, click and open tracking, where your ESP wants clicks to pass through their domain under your brand name. Second, DKIM setup, where some ESPs ask you to create a CNAME pointing to their managed DKIM selector so they can rotate keys without your involvement. Third, subdomain delegation to third-party services like Postmark or Twilio SendGrid for specific sending streams.
A few things to know before you add one. CNAMEs can't sit at your root domain (tidalmail.com itself), only on subdomains like tracking.tidalmail.com. They also can't share a name with other record types (no MX or TXT at the same hostname). And each CNAME adds one extra DNS lookup hop, which is rarely a problem in practice but worth knowing if you're stacking multiple redirects.
If you want to see how your CNAME is resolving right now, our free Email Header Analyzer can help you trace what's actually happening at the DNS level. Or if your tracking setup is giving you grief, the SOS hotline is free and we're happy to look at it with you.
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