How to Set Up SPF, DKIM & DMARC for Postmark

Sending email through Postmark 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 Postmark'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

SPF tells receiving servers that Postmark is authorized to send email for your domain. Add this TXT record at your root domain:

Name:  @  (your domain, e.g. yourdomain.com) Type:  TXT Value: v=spf1 include:spf.mtasv.net ~all

If you already send through another provider (Google Workspace, Microsoft 365, a CRM), you must have one SPF record that includes all of them, for example:

v=spf1 include:spf.mtasv.net include:_spf.google.com -all

Once you're confident every sending service is listed, switch the trailing ~all to -all (hardfail) for stronger protection. Watch the 10-DNS-lookup limit — too many includes causes an SPF permerror.

Tip: Postmark occasionally updates its sending infrastructure — confirm the exact include value in your Postmark dashboard before publishing.

Step 2: Enable and publish DKIM

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

1. Open Postmark's domain / sender authentication settings
2. Enable DKIM (or "authenticate domain")
3. Copy the DKIM record Postmark shows you — usually at a selector like pm (Postmark generates the exact selector)._domainkey
4. Add it to your DNS provider exactly as shown (TXT or CNAME)
5. Return to Postmark and click verify once DNS has propagated

DKIM won't activate until Postmark 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 Postmark 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.

Postmark-specific gotchas

• Postmark requires you to verify a Sender Signature or domain before it will send. Add the DKIM record it generates under Sending → Domains.
• For full DMARC alignment, set a custom Return-Path (a CNAME Postmark provides) so SPF aligns with your domain, not Postmark's.
• Postmark only sends transactional mail — do not point bulk/marketing campaigns at it or your account may be paused.

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.