Postmark: custom domain readiness

Postmark is transactional-first and strict about quality, which makes setup short: one DKIM record, one Return-Path CNAME, and your own DMARC.

1 · Add the DKIM record

In Postmark: Sender Signatures → your domain → DKIM. Postmark generates a TXT record with a unique selector (it looks like 20240115...pm._domainkey.yourdomain.com). Publish it and verify. Your mail is then signed with d=yourdomain.com — DKIM-aligned for DMARC.

2 · Set a custom Return-Path

Add the CNAME Postmark shows, typically pm-bounces.yourdomain.com → pm.mtasv.net, and set it as your custom Return-Path. This makes the envelope-from your own subdomain so SPF aligns too — without touching your root SPF record.

3 · Publish DMARC

Even pure-transactional senders should publish DMARC at _dmarc.yourdomain.com:

TXT record on _dmarc.yourdomain.com

v=DMARC1; p=none; rua=mailto:dmarc-reports@yourdomain.com

Outlook's 2025 high-volume requirements and Gmail's bulk rules both expect DMARC. With Postmark's aligned DKIM + SPF, you can usually move to p=reject faster than marketing senders.

Common pitfalls

Adding include:mtasv.net to your root SPF — not needed once the custom Return-Path CNAME is in place.
Sending marketing through Postmark's transactional stream — use the broadcast stream (with unsubscribe headers) or a dedicated marketing ESP.
Forgetting DMARC because “it's only receipts” — spoofers love clean transactional domains.

Verify it worked

Run a free scan to confirm SPF/DMARC are live, then send yourself a campaign and paste its headers to verify DKIM alignment and one-click unsubscribe end-to-end.

Scan your domain Analyze a test email

Establishing signal

3 · Publish DMARC

Even pure-transactional senders should publish DMARC at _dmarc.yourdomain.com:

TXT record on _dmarc.yourdomain.com

v=DMARC1; p=none; rua=mailto:dmarc-reports@yourdomain.com

Outlook's 2025 high-volume requirements and Gmail's bulk rules both expect DMARC. With Postmark's aligned DKIM + SPF, you can usually move to p=reject faster than marketing senders.

Common pitfalls

Adding include:mtasv.net to your root SPF — not needed once the custom Return-Path CNAME is in place.
Sending marketing through Postmark's transactional stream — use the broadcast stream (with unsubscribe headers) or a dedicated marketing ESP.
Forgetting DMARC because “it's only receipts” — spoofers love clean transactional domains.