Zone apex
The top name of a DNS zone, such as example.com itself rather than www.example.com, where the zone's SOA and NS records live.
What it means
RFC 9499 defines the apex as the name that owns a zone's SOA and authoritative NS records. For most domains that is the registered domain, example.com.
Two mail facts depend on it. SPF records and the MX records for addresses like you@example.com sit at the apex. And a CNAME cannot be placed there, because a CNAME may not share a name with other records, while the apex must hold SOA and NS. Some DNS hosts offer flattened alias records to work around that, such as Cloudflare's CNAME flattening, but those are provider features, not standard DNS.
DMARC records are not at the apex but at _dmarc below it.
Related terms
On this site
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- RFC 9499: DNS Terminology, section 7rfc-editor.org
- RFC 1034: Domain Names: Concepts and Facilities, section 3.6.2rfc-editor.org
- Cloudflare docs: CNAME flatteningdevelopers.cloudflare.com
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