In Postmark, go to Sender Signatures and add your domain. Postmark generates a DKIM CNAME record with a unique selector. Add this CNAME to your DNS, then click Verify in Postmark. Once confirmed, Postmark signs all outbound email with a 2048-bit DKIM key aligned to your domain.
DKIM for Postmark: Setup Guide
Add Your Domain in Postmark
- Log into Postmark and go to Sender Signatures
- Click Add Domain
- Enter your sending domain
- Postmark generates DNS records for DKIM and return-path
Add the DKIM CNAME
Postmark provides a CNAME record:
Host: [selector]._domainkey.yourdomain.com
Type: CNAME
Value: Points to Postmark's DKIM infrastructure
Copy the exact hostname and value from the Postmark dashboard. The CNAME approach means Postmark handles key rotation — you set it up once.
Practitioner note: Postmark is one of the best ESPs at making authentication simple. Their onboarding literally won't let you move forward without setting up DKIM. More ESPs should work this way.
Verify the Record
Click Verify next to DKIM in the Sender Signatures page. If DNS has propagated, you'll see a green confirmed status.
If verification fails, check:
- DNS propagation (wait 15 min to a few hours)
- No duplicate domain in the hostname
- CNAME record, not TXT
Postmark's Return-Path Record
Postmark also asks you to set up a custom return-path record. This is separate from DKIM but equally important — it handles SPF alignment and bounce processing.
Add both the DKIM CNAME and the return-path CNAME. They're both required for full authentication.
Verify in Email Headers
Send a test message through Postmark and check headers:
Authentication-Results: mx.google.com;
dkim=pass [email protected]
Practitioner note: Postmark's transactional email focus means they maintain extremely high sending reputation. Pairing their infrastructure with proper DKIM authentication on your domain gives you the best possible delivery rates for password resets, receipts, and notifications.
Postmark is typically used alongside another ESP for marketing email. If you need help getting authentication aligned across Postmark plus your marketing sender, schedule a consultation.
Sources
- Postmark: Adding a sender signature
- Postmark: DKIM authentication
- RFC 6376: DomainKeys Identified Mail (DKIM) Signatures
- MXToolbox: DKIM Record Lookup
v1.0 · April 2026
Frequently Asked Questions
How do I set up DKIM in Postmark?
Go to Sender Signatures, add your domain, and Postmark gives you a CNAME record. Add it to DNS and verify in Postmark.
Does Postmark handle DKIM key rotation?
Yes. Since Postmark uses CNAME records, they manage key rotation on their infrastructure. You never need to update DNS after the initial setup.
What DKIM selector does Postmark use?
Postmark uses a unique selector per account, typically in the format of a date-based or hash-based prefix at _domainkey.yourdomain.com.
Does Postmark require a dedicated sending domain?
Postmark strongly recommends domain authentication with DKIM. You can send without it, but emails will be signed with Postmark's domain, hurting DMARC alignment.
Can I use Postmark with a subdomain?
Yes. Postmark supports subdomain authentication. Each subdomain needs its own Sender Signature entry and DKIM CNAME record.
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