What is a CNAME (Canonical Name) record?

A CNAME (Canonical Name) record creates an alias from one hostname to another:

tracking.tidalmail.com CNAME links.emailprovider.com

When someone looks up tracking.tidalmail.com, DNS returns the target, and the lookup continues from there.

Email uses:

Tracking domain setup for click and open tracking.

Delegating DKIM selectors to ESP-managed records.

Pointing subdomains to service providers.

Limitations:

Cannot coexist with other records at the same name (except in some modern implementations).

Cannot be used at the apex (naked domain) with most providers.

Adds an extra DNS lookup.

An alias in the registry. Look up this name, but follow the redirect to the real entry.