How to Set Up SPF, DKIM & DMARC for Resend

Sending email through Resend does not authenticate your domain on its own. Until you publish SPF, DKIM, and DMARC, receiving servers like Gmail, Outlook, and Yahoo can't confirm your mail is really from you — so it lands in spam, or since the 2024 Gmail/Yahoo bulk-sender rules, gets rejected outright. This guide covers the complete setup, in order.

What you'll set up

• SPF — authorizes Resend's servers to send as your domain
• DKIM — cryptographically signs every message so it can't be forged
• DMARC — tells receivers what to do if SPF or DKIM fail, and sends you reports

Step 1: Add SPF

Resend authenticates through a delegated sending subdomain rather than a manual SPF include on your root domain. In your Resend account, start the domain authentication flow and it will generate a set of records — typically a CNAME (and sometimes an SPF TXT) for a subdomain like send.yourdomain.com.

Add every record Resend shows you, exactly as displayed. Because the values are specific to your account, copy them from the dashboard rather than guessing.

Step 2: Enable and publish DKIM

DKIM adds a cryptographic signature to every message. Resend generates a unique key pair and gives you a DNS record to publish the public half.

1. Open Resend's domain / sender authentication settings
2. Enable DKIM (or "authenticate domain")
3. Copy the DKIM record Resend shows you
4. Add it to your DNS provider exactly as shown (TXT or CNAME)
5. Return to Resend and click verify once DNS has propagated

DKIM won't activate until Resend confirms the record is live, so allow 15–60 minutes for propagation before verifying.

Step 3: Add DMARC

DMARC ties SPF and DKIM together and tells receiving servers what to do when a message fails both. Start in monitor-only mode so you can review reports before enforcing:

Name:  _dmarc Type:  TXT Value: v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com

Replace the rua address with a mailbox you can read — that's where daily aggregate reports go. Or point it at a free EmailHealth DMARC inbox and we'll parse the XML into a readable per-sender breakdown.

Step 4: Verify it's all passing

After the records propagate, send a test through Resend and confirm authentication:

• SPF: the receiving server shows spf=pass
• DKIM: the raw headers show dkim=pass with your domain
• DMARC: dmarc=pass once SPF or DKIM aligns to your domain

The fastest way is to run a free EmailHealth domain check — it confirms all three at once and scores your overall deliverability.

Resend-specific gotchas

• Resend gives you a set of records (an MX, an SPF TXT, and a DKIM record) for a sending subdomain such as send.yourdomain.com — add all of them exactly as shown in the Resend dashboard.
• Because Resend sends from a subdomain, your root-domain DMARC policy still applies through the organizational domain.
• Resend builds on Amazon SES infrastructure, so its SPF record references SES — use the exact value Resend displays rather than guessing.

Step 5: Progress to enforcement

After 1–2 weeks at p=none with clean reports, tighten your DMARC policy: move to p=quarantine; pct=25, increase gradually, then p=rejectonce no legitimate mail is being caught. That's when spoofing of your domain actually stops.