SendGrid Email Authentication Guide

Before you start

• You need access to the DNS settings for your domain. This is usually at your domain registrar or DNS provider (Cloudflare, Namecheap, GoDaddy, etc.).
• You need admin or settings access to your SendGrid account to generate DKIM keys and verify records.
• DNS changes take time to propagate. After saving a record, wait at least 15-30 minutes before testing.

SPF Setup for SendGrid

SPF (Sender Policy Framework) is a DNS TXT record that lists which mail servers are allowed to send email on behalf of your domain. Receiving servers check it to decide whether to accept or flag your mail.

SendGrid uses CNAME-based domain authentication instead of a plain SPF TXT record. When you authenticate a domain in SendGrid, it creates a branded subdomain (like em.yourdomain.com) that handles SPF through CNAME delegation.

SendGrid uses CNAME-based domain authentication

Instead of a plain TXT record, SendGrid provides 6 CNAME records through its Sender Authentication wizard. These cover both SPF and DKIM in one flow.

Steps

1. In SendGrid, go to Settings → Sender Authentication → Authenticate Your Domain.
2. Enter your domain. SendGrid generates the CNAME records for you - follow the wizard.
3. You add up to 6 CNAME records that SendGrid provides in the Sender Authentication wizard. SendGrid's system resolves SPF through those CNAMEs automatically.
4. Add all the CNAME records to your DNS provider, then return to SendGrid and click Verify.

DKIM Setup for SendGrid

DKIM (DomainKeys Identified Mail) adds a cryptographic signature to outgoing email. Receiving servers verify the signature against a public key you publish as a DNS TXT record. A valid DKIM signature proves the message was not altered in transit and that it came from an authorized sender.

Selector for SendGrid: s1 and s2 (CNAME records pointing to SendGrid's key infrastructure)

Steps

1. In SendGrid, go to Settings → Sender Authentication → Authenticate Your Domain.
2. Enter your domain. SendGrid generates 6 DNS records: 2 CNAME records for DKIM and 4 more for SPF and tracking.
3. Add all 6 CNAME records to your DNS provider exactly as shown. The DKIM records look like s1._domainkey.yourdomain.com → s1.domainkey.uXXXX.wl.sendgrid.net.
4. Return to SendGrid and click Verify. All 6 CNAMEs must resolve before domain authentication is complete.

Verify DKIM

• Send a test email to a Gmail address and open it. Click the three-dot menu → "Show original". Look for dkim=pass in the authentication results.
• From the command line:
  

  dig TXT selector._domainkey.yourdomain.com +short

• Or use the InboxGreen DKIM checker.

DMARC Setup for SendGrid

DMARC (Domain-based Message Authentication, Reporting, and Conformance) ties SPF and DKIM together. It tells receiving servers what to do with mail that fails both checks, and sends you reports about who is sending email on behalf of your domain. DMARC also requires alignment: the domain in your visible From header must match the domain authenticated by SPF or DKIM.

SendGrid domain authentication automatically handles DMARC alignment when you use a custom authenticated sending domain. Sending from sendgrid.net as your From domain will fail DMARC.

The three-stage approach

Stage	DNS value	When to use it
Monitor	v=DMARC1; p=none; rua=mailto:[email protected]; fo=1	Start here. Collects reports without blocking any mail.
Quarantine	v=DMARC1; p=quarantine; pct=25; rua=mailto:[email protected]; fo=1	After 2-4 weeks at p=none with clean reports. Sends some failing mail to spam.
Reject	v=DMARC1; p=reject; pct=100; rua=mailto:[email protected]; fo=1	Full protection once SPF and DKIM alignment is verified.

Publish the DMARC record

1. Create a TXT record at host _dmarc (not @) with the p=none value above.
2. Replace [email protected] with a real inbox that can receive XML report emails.
3. Wait for DNS propagation, then verify with dig TXT _dmarc.yourdomain.com +short.
4. After 2-4 weeks, review the reports and tighten the policy when alignment looks healthy.

List-Unsubscribe for SendGrid

The List-Unsubscribe header gives inbox providers like Gmail and Outlook a machine-readable way to offer a one-click unsubscribe button. When it is present and valid, Gmail shows an "Unsubscribe" link next to the sender name without the recipient needing to scroll to the bottom of the email. This reduces spam complaints and protects your sender reputation.

How to enable it

1. In your sending platform or email template, enable the List-Unsubscribe header option. Most platforms (SendGrid, Mailgun, Brevo, Shopify Email) have a toggle or a macro for this.
2. Use a one-click HTTPS unsubscribe URL as the primary method. Include a mailto: address as fallback.
3. Add the List-Unsubscribe-Post header to declare one-click support (required by Gmail's February 2024 guidelines for senders above 5,000 messages/day).

Example headers

List-Unsubscribe: <https://yourdomain.com/unsubscribe/TOKEN>, <mailto:[email protected]?subject=unsubscribe>
List-Unsubscribe-Post: List-Unsubscribe=One-Click

Common mistakes

• Using a broken or expired token in the unsubscribe URL. Inbox providers test the link periodically.
• Only providing a mailto: link without a one-click HTTPS URL. Gmail and Outlook prefer the HTTPS method.
• Not honoring the unsubscribe request immediately. Gmail requires that one-click unsubscribes are processed within two business days.

To verify, send a test email to a Gmail address and look at "Show original". You should see the List-Unsubscribe header in the raw message headers.

Verify All Four Records

After publishing all records, run these checks:

Record	Command	What to look for
SPF	dig TXT yourdomain.com +short	One TXT record starting with v=spf1
DKIM	dig TXT selector._domainkey.yourdomain.com +short	A TXT record starting with v=DKIM1
DMARC	dig TXT _dmarc.yourdomain.com +short	A TXT record starting with v=DMARC1
All three	InboxGreen Free Check	Green pass on SPF, DKIM, and DMARC

Common Mistakes with SendGrid

• Adding a separate <code>v=spf1 include:sendgrid.net ~all</code> TXT record instead of using CNAME-based domain authentication.
• Only adding some of the 6 CNAME records and wondering why domain verification stays pending.
• Sending from <code>[email protected]</code> as the visible From address instead of your own authenticated domain.

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