DMARC (RFC 7489) tells receiving mail servers what to do when a message claiming to be from your domain fails SPF or DKIM. You publish exactly one DMARC record at `_dmarc.<your-domain>`, regardless of which ESP you use — DMARC is a domain-level policy, not a per-sender configuration. Postmark doesn't run DMARC for you, but their SPF + DKIM setup is what makes your DMARC checks pass.
Start every domain at `p=none` with a `rua` (aggregate report) address pointing somewhere you actually read. Watch the reports for two to four weeks to confirm 100% of legitimate mail is aligned, then progress to `p=quarantine` and finally `p=reject`. Skipping the monitoring step is the single most common way founders accidentally block their own mail.
Publish these DNS records
Add the following record(s) to your domain's DNS zone. Most registrars (Cloudflare, Route 53, Namecheap, GoDaddy) accept values exactly as shown.
- Type
TXT- Host
_dmarc- Value
v=DMARC1; p=none; rua=mailto:[email protected]
- Postmark only sends transactional mail and signs with your domain's DKIM, so DMARC alignment is straightforward — most accounts can progress to `p=reject` quickly.
Where in Postmark
The DMARC configuration lives in Postmark → Sender Signatures → Add Domain → DNS.
Verify the records
Once published, run the DMARC Checker on your apex domain to confirm the record parses, reporting URIs are valid, and the policy is what you intended.
dig +short TXT _dmarc.your-domain.comCommon pitfalls
- Postmark's anti-spam team will pause your account if you send marketing mail through it. Use a separate ESP for newsletters or promotional content.
- The Return-Path on Postmark mail is `pm.mtasv.net` by default. Set up a custom Return-Path domain for SPF alignment if you need DMARC to pass on SPF as well as DKIM.