DNS guide

CNAME Record Setup Guide

A CNAME record maps one hostname to another. Email providers use CNAMEs for DKIM alignment. But CNAMEs have important restrictions — using them in the wrong place breaks email.

Key restriction

You cannot use a CNAME at your root domain (@). CNAMEs at the apex conflict with SOA and NS records — and would override your MX records, breaking email delivery entirely.

Common CNAME uses

SendGrid DKIM alignment

s1._domainkey.yourdomain.com CNAME s1.domainkey.u123.wl.sendgrid.net

Microsoft 365 DKIM

selector1._domainkey.yourdomain.com CNAME selector1-yourdomain-com._domainkey.yourtenant.onmicrosoft.com

Subdomain to service

app.yourdomain.com CNAME yourapp.herokuapp.com

Verify CNAME propagation

Open Propagation checker →
Related: CNAME record · Subdomain takeover

Step by step

Step 1 Identify the hostname you need the CNAME on — must be a subdomain, never @.
Step 2 Check no other records exist at that hostname (A, MX, TXT) — CNAMEs can't coexist.
Step 3 Add the CNAME record with source hostname and target hostname.
Step 4 Verify with Propagation checker — select CNAME type.

FAQ

What is a CNAME record?

A DNS record that points 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 at the apex (root) domain — they conflict with required records and break email. Use an A record or ALIAS/ANAME instead.

Can I have other records at the same hostname as a CNAME?

No. A CNAME is exclusive — no other record types can exist at the same hostname.

Why do email providers use CNAMEs for DKIM?

CNAMEs let the provider rotate DKIM keys without you updating DNS. Your CNAME always points to their current key.

How do I verify a CNAME is working?

Use DomainPreflight Propagation checker — select CNAME, enter the full subdomain, confirm the target appears.

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