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Mailgun Webhooks

TL;DR

To integrate Mailgun webhooks with ngrok:

  1. Launch your local webhook. npm start
  2. Launch ngrok. ngrok http 3000
  3. Configure Mailgun webhooks with your ngrok URL.
  4. Secure your webhook requests with verification.

This guide covers how to use ngrok to integrate your localhost app with Mailgun by using Webhooks. Mailgun webhooks can be used to notify an external application whenever specific events occur in your Mailgun account.

By integrating ngrok with Mailgun, you can:

  • Develop and test Mailgun webhooks locally, eliminating the time in deploying your development code to a public environment and setting it up in 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 and without spending time reproducing events manually in your Mailgun account.
  • Secure your app with Mailgun validation provided by ngrok. Invalid requests are blocked by ngrok before reaching your app.

Step 1: Start your app​

For this tutorial, we'll use the sample NodeJS app available on GitHub.

To install this sample, run the following commands in a terminal:

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This will get the project installed locally.

Now you can launch the app by running the following command:

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The app runs by default on port 3000.

You can validate that the app is up and running by visiting http://localhost:3000. The application logs request headers and body in the terminal and responds with a message in the browser.

Step 2: Launch ngrok​

Once your app is running successfully on localhost, let's get it on the internet securely using ngrok!

  1. If you're not an ngrok user yet, just sign up for ngrok for free.

  2. Download the ngrok agent.

  3. Go to the ngrok dashboard and copy your Authtoken.
    Tip: The ngrok agent uses the auth token to log into your account when you start a tunnel.

  4. Start ngrok by running the following command:

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  5. ngrok will display a URL where your localhost application is exposed to the internet (copy this URL for use with Mailgun). ngrok agent running

Step 3: Integrate Mailgun​

To register a webhook on your Mailgun account follow the instructions below:

  1. Access Mailgun and sign in using your Mailgun account.

  2. On the Dashboard page, click Sending in the left menu, click Webhooks and then click Add webhook.

  3. On the New webhook popup, select Delivered Messages in the Event type field, and enter the URL provided by the ngrok agent to expose your application to the internet in the URL field (i.e. https://1a2b-3c4d-5e6f-7g8h-9i0j.ngrok.app). Webhook URL

  4. Click Create webhook.

To test the webhook follow the instructions below:

  1. On the Webhooks page, select Delivered Messages in the Event type combobox, enter the ngrok URL in the URL to test field, and then click Test webhook.

    Confirm your localhost app receives the event notification and logs both headers and body in the terminal. Also, confirm a Response message appears on the Webhooks page.

Run Webhooks with Mailgun and ngrok​

Mailgun sends different request body contents depending on the event that is being triggered. You can trigger new calls from Mailgun to your application by following the instructions below.

  1. Access the Mailgun Dashboard, click Sending in the left menu, and then click Overview.

  2. Enter a valid email address in the Email address field in the Authorized Recipients section, and then click Save Recipient.

Verify the recipient receives an email from Mailgun asking to agree to receive emails from your Mailgun account, click the I Agree link in the body of the email and then click Yes.

  1. In the Mailgun Dashboard, click Select in the API tile and choose one of the options that appears on the screen to send emails. For example, open a terminal window and run the following command using curl:

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    Note: Replace the following with values from your Mailgun account:

    • API_BASE_URL: API base URL value that appears on the Overview page.
    • API_KEY: API Key value that appears on the Overview page.
    • YOUR_DOMAIN: Find your domain by clicking Domains in the left menu.
    • AUTHORIZED_RECIPIENT: the Email address you registered as an authorized recipient.

    Confirm your localhost app receives an event notification and logs both headers and body in the terminal.

Inspecting requests​

ngrok's Traffic Inspector captures all requests made through your ngrok endpoint to your localhost app. Click on any request to view detailed information about both the request and response.

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By default, accounts only collect traffic metadata to avoid exposing secrets. 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

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. Modify the request (optional): 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.

Secure webhook requests​

The ngrok signature webhook verification feature allows ngrok to assert that requests from your Mailgun webhook are the only traffic allowed to make calls to your localhost app.

Note: This ngrok feature is limited to 500 validations per month on free ngrok accounts. For unlimited, upgrade to Pro or Enterprise.

This is a quick step to add extra protection to your application.

  1. Access Mailgun and sign in using your Mailgun account.

  2. On the Dashboard page, click Sending in the left menu and then click Webhooks.

  3. On the Webhooks page, click the eye icon near the HTTP webhook signing key text and copy the value that appears.

  4. Create a file named mailgun_policy.yml, replacing {webhook signing key} with the value you have copied before:

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  5. Restart your ngrok agent by running the command:

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  6. Access Mailgun and send a new email to an authorized recipient.

Verify that your local application receives the request and logs information to the terminal.