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This guide walks you through using ngrok to receive Mailgun webhooks on your localhost app. By integrating ngrok with Mailgun, you can:
  • Develop and test Mailgun webhooks locally without deploying to a public environment or setting up HTTPS.
  • Inspect and troubleshoot requests from Mailgun in real time via the inspection UI and API.
  • Modify and replay Mailgun webhook requests with a single click instead of reproducing events manually in your Mailgun account.
  • Secure your app with Mailgun webhook validation provided by ngrok. Invalid requests are blocked by ngrok before reaching your app.

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What you’ll need

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1. Start your app

For this tutorial, you can use the sample Node.js app on GitHub. To install the sample, run the following in a terminal: 
git clone https://github.com/ngrok/ngrok-webhook-nodejs-sample.git
cd ngrok-webhook-nodejs-sample
npm install
Then start the app: 
npm start
The app runs on port 3000 by default. You can confirm it’s running by visiting http://localhost:3000. The app logs request headers and body in the terminal and shows a message in the browser.

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2. Expose your app with ngrok

Once your app is running locally, you’re ready to put it online securely using ngrok.
The ngrok agent uses your authtoken to authenticate when you start a tunnel.
  • Start ngrok: 
    ngrok http 3000
  • Copy the URL ngrok displays. Your app is now exposed at that URL for use with Mailgun.

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3. Configure Mailgun to send webhooks

Mailgun can send webhook requests to your app when events occur in your account. To register for those events:
  • Sign in to Mailgun.
  • Click Sending, Webhooks, and then Add webhook.
  • On the New webhook popup, select Delivered Messages in Event type, enter your ngrok URL in URL (for example, https://1a2b-3c4d-5e6f-7g8h-9i0j.ngrok.app).
  • Click Create webhook.
To test: on the Webhooks page, select Delivered Messages, enter your ngrok URL in URL to test, and click Test webhook. Confirm your localhost app receives the event and logs both headers and body in the terminal, and that a Response appears on the Webhooks page.

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Run webhooks with Mailgun and ngrok

Mailgun sends different request body contents depending on the event. To trigger new calls from Mailgun to your app:
  • In the Mailgun Dashboard, go to Sending and Overview.
  • In Authorized Recipients, enter a valid email and click Save Recipient.
  • Have the recipient confirm by clicking the link in the email from Mailgun.
  • Send an email (for example, via the Mailgun API). Replace placeholders with values from your account (API base URL and API Key from Overview, your domain from Domains, and the authorized recipient email): 
    curl --location --request POST 'API_BASE_URL/messages' \
--header 'Authorization: Basic api:API_KEY' \
--form 'from="mailgun@YOUR_DOMAIN"' \
--form 'to="AUTHORIZED_RECIPIENT"' \
--form 'subject="Hello from Mailgun"' \
--form 'text="Testing some Mailgun email!"'
Confirm your localhost app receives the event and logs both headers and body in the terminal.

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Inspecting requests

ngrok’s Traffic Inspector captures all requests made through your ngrok endpoint to your localhost app. Select any request to view detailed information about both the request and response.
To avoid exposing secrets, accounts only collect traffic metadata by default. You must enable full capture in the Observability section of your account settings to capture complete request and response data.
Use the traffic inspector to:
  • Validate webhook payloads and response data
  • Debug request headers, methods, and status codes
  • Troubleshoot integration issues without adding logging to your app

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Replaying requests

Test your webhook handling code without triggering new events from your service using the Traffic Inspector’s replay feature:
  1. Send a test webhook from your service to generate traffic in your Traffic Inspector.
  2. Select the request you want to replay in the traffic inspector.
  3. Choose your replay option:
    • Click Replay to send the exact same request again
    • Select Replay with modifications to edit the request before sending
  4. (Optional) Modify the request: Edit any part of the original request, such as changing field values in the request body.
  5. Send the request by clicking Replay.
Your local application will receive the replayed request and log the data to the terminal.

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Secure webhook requests

ngrok can verify that incoming requests are from your Mailgun webhook so only that traffic reaches your app.
Webhook verification is limited to 500 validations per month on free accounts. If you need more, you can upgrade to Hobbyist or Pay-as-you-go. See TPU Pricing for details.
To add verification:
  • In Mailgun, go to Sending and Webhooks.
  • Click the eye icon next to HTTP webhook signing key and copy the value.
  • Create a Traffic Policy file named mailgun_policy.yml. Replace {webhook signing key} with the value you copied: 
    on_http_request:
  - actions:
      - type: verify-webhook
        config:
          provider: mailgun
          secret: "{webhook signing key}"
  • Restart ngrok with the policy file: 
    ngrok http 3000 --traffic-policy-file mailgun_policy.yml
  • Send a new email to an authorized recipient to trigger the webhook.
Your app should receive the request and log it in the terminal.