Glossary
CNAME Record — What It Is and How to Use It
A CNAME (Canonical Name) record is a DNS record that maps one domain name to another. Instead of pointing to an IP address directly, a CNAME points to another hostname whose IP is resolved separately. Email providers like SendGrid and Microsoft 365 use CNAME records for DKIM alignment — your CNAME points to their servers, letting them sign email with your domain.
CNAME vs A Record
- A record: hostname → IP address
- CNAME record: hostname → another hostname
CNAME Restrictions
- Cannot be used at root domain (@) — use A record or ALIAS/ANAME instead
- Cannot coexist with other record types at the same hostname
- Avoid CNAME chains (CNAME → CNAME → CNAME)
Check DNS after you publish records
Open DNS Preflight →FAQ
What is a CNAME record?
A DNS record that maps one hostname to another hostname instead of directly to an IP address.
Can I use a CNAME at my root domain?
No. CNAMEs cannot be used at the apex (root) domain because they would conflict with required SOA and NS records. Use an A record or ALIAS/ANAME instead.
Why do email providers use CNAMEs for DKIM?
CNAMEs let providers control the DKIM key on their end — they can rotate keys without you updating DNS. Your CNAME always points to their current key.