CNAME
Canonical Name
A CNAME record creates an alias pointing to another hostname. Learn why CNAMEs cannot be used for MX or at the domain root, and when they appear in DKIM setups.
Record Type
CNAME
Category
Address & Routing
Address & Routing
RFC
RFC 1035
RFC 1035
Email Relevant
Yes
Yes
Format
CNAME <target-hostname>.
Example
CNAME mail.example.com.
TTL Guidance
3600 s; note that resolvers chase the chain — the final A/AAAA TTL governs caching
3600 s; note that resolvers chase the chain — the final A/AAAA TTL governs caching
💬 What This Record Does
A CNAME (Canonical Name) record creates an alias: it says "this hostname is really just another name for that hostname." When a resolver sees a CNAME, it follows the chain until it reaches an A or AAAA record. CNAMEs are commonly used to alias subdomains (www → example.com) or to delegate DKIM selector lookups to a provider's infrastructure without copying the full public key.
Common Uses
- DKIM selector delegation: some ESPs let you point selector._domainkey.example.com via CNAME to their key
- Aliasing subdomains to a CDN or hosting provider
- Domain ownership verification using a provider-generated CNAME
⚠️ Watch Out For
- You CANNOT use a CNAME at the domain root (example.com itself) — RFC prohibits it and it would break MX and other records.
- MX records cannot point to a CNAME target — only to a hostname with a direct A/AAAA record.
- A CNAME cannot coexist with any other record type on the same name (except DNSSEC RRSIG).