Postmark: DKIM and Return-Path CNAMEs.

22 October 2026

This guide covers Postmark: where to copy SPF and DKIM values, how to publish them at your DNS provider, and how to point DMARC aggregate reports at a mailbox you control—or at Hosted DMARC on Sender Identity.

Before you change DNS

Run the free static audit and keep a copy of the current SPF and DMARC text.
List every system that already sends as this domain (office mail, billing, marketing, tickets).
Prefer one organizational-domain DMARC record. Subdomain records override the org policy when present.

Where to copy the values

Postmark → Sender Signatures or Domains.
Open the domain. Postmark lists a DKIM CNAME and a Return-Path CNAME (SPF via that bounce domain).
Publish both. Wait until Postmark marks DNS as verified.

Typical DNS shape

Type	Name / host	Value / points to	Note
`TXT`	`@`	`v=spf1 include:spf.mtasv.net -all`	Merge with existing includes; stay under 10 DNS lookups.
`CNAME`	`(selector)._domainkey`	`pm.mtasv.net (example)`	Exact values appear in Postmark.
`CNAME`	`pm-bounce (or shown host)`	`pm.mtasv.net`	Return-Path / SPF alignment helper.

DMARC aggregate reports

Two workable patterns:

Self-hosted mailbox. Publish v=DMARC1; p=none; rua=mailto:dmarc@brand.example on _dmarc.brand.example. The mailbox host must share the organizational domain, or you must authorize an external report host with a v=DMARC1 TXT at brand.example._report._dmarc.<report-host>.
Hosted DMARC. Remove the TXT at _dmarc, publish a CNAME to brand.example._dmarc.hosted.senderidentity.com, and let Sender Identity open a report mailbox at reports.senderidentity.com. Stages move only when you approve them: p=none, then p=quarantine at 25% and 50%, then p=reject.

The free audit suggests a starter p=none record for your own mailbox. It never writes p=reject and never points rua at reports.senderidentity.com—that only happens on the paid hosted path.

Verify

Wait for DNS, then run the free audit. Add any unusual DKIM selector under “DKIM selectors” if the default probe list misses it.
Sender Identity’s vendor catalog can label known includes and selectors in paid monitoring; labels never publish DNS for you.
Keep p=none until aggregate reports show only senders you recognize, then stage quarantine and reject in Account.