How to Test Postmark Webhooks
Postmark webhooks notify your application about email delivery, bounce, spam complaint, and link tracking events.
Looking for the broader picture? See the 7 best webhook testing tools (2026), or if you're already on Webhook.site, the 60-second migration to HookRay.
Postmark Official Webhook Docs1. Postmark Webhook Events
Postmark can send the following webhook events to your endpoint:
DeliveryBounceSpamComplaintOpenClickSubscriptionChange2. Set Up a Test Endpoint with HookRay
Follow these steps to start receiving Postmark webhooks for testing:
- Go to HookRay and click "Start Testing — Free" to get your unique webhook URL.
- Copy the URL (e.g.,
https://h.hookray.com/abc123). - In your Postmark dashboard, navigate to the webhook settings and paste the HookRay URL as your endpoint.
- Select the events you want to receive (see list above).
- Trigger a test event — HookRay will show the incoming webhook in real-time.
3. Sample Postmark Webhook Payload
Here's an example of what a Postmark webhook payload looks like:
{
"RecordType": "Delivery",
"ServerID": 23,
"MessageStream": "outbound",
"MessageID": "883953f4-6105-42a2-a16a-77a8eac79483",
"Recipient": "user@example.com",
"Tag": "welcome-email",
"DeliveredAt": "2026-03-20T17:00:00Z",
"Details": "Test delivery"
}4. Frequently Asked Questions
How do I test Postmark webhooks without deploying?
Use HookRay to get an instant public webhook URL. Paste it into your Postmark dashboard's webhook configuration, trigger an event, and watch the payload arrive in real time. No code, no ngrok, no deployment required. The free tier captures 100 requests per month and works on all Postmark event types.
Why aren't my Postmark webhooks arriving?
The four most common causes: (1) the endpoint URL isn't publicly accessible — Postmark can't reach localhost; (2) the wrong events are subscribed in your Postmark dashboard; (3) signature verification is rejecting the request before your handler runs; (4) Postmark can't reach your server because of a firewall, expired SSL certificate, or wrong DNS. Use HookRay's URL to isolate which of these four is failing — if HookRay receives the webhook, the problem is in your handler. If HookRay doesn't, the problem is in Postmark configuration.
Why am I getting 400 or 500 errors from my Postmark webhook?
Postmark reports the response status your endpoint returned. HookRay accepts any payload and returns 200 OK by default, so if you see 400/500 in your Postmark dashboard while pointing at HookRay, the issue is in Postmark's configuration (wrong event, malformed signing secret, etc.). If you point at your own endpoint and get 400/500, the issue is in your handler — capture the request with HookRay, replay it locally, and debug from the captured payload.
How do I verify Postmark webhook signatures?
Postmark signs each webhook request with a shared secret. Capture the raw headers and body using HookRay, then verify the signature in your application using Postmark's SDK or a standard HMAC library. Once verification works against HookRay-captured data, you can safely deploy. Postmark's docs (linked above) cover the exact signing algorithm.
Can I replay a captured Postmark webhook?
Yes — HookRay's replay feature re-sends any captured webhook to a different endpoint with one click. This is the fastest way to fix a buggy handler: capture the payload once, fix your code, and replay until it works. No need to re-trigger the event in Postmark.
5. Next Steps
- Use HookRay's webhook replay feature to re-send captured webhooks while building your handler
- Enable smart parsing (Pro plan) to see Postmark-specific fields highlighted automatically
- Check the Postmark webhook documentation for the complete event reference
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One-page reference for 50+ APIs — canonical events, signing methods, sample payloads. Print it, pin it, share it.
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