Send a welcome email from Auth0

Auth0 runs your code itself, so this one needs no webhook route. A post-user-registration Action calls Courier straight from Auth0.

What you will build

Prerequisites

An Auth0 tenant with a Database or Passwordless connection
A published to send

How this differs from a webhook

Clerk and Stripe post to a route you host, so you verify a signature and run your own code. Auth0 Actions are your code, running inside Auth0. Three consequences follow. No route, no signature, no tunnel. There is nothing public to host and nothing to verify, because nothing crossed the internet to reach you. Local development needs no ngrok. Secrets live in the Action. Auth0 stores them and exposes them as event.secrets, so your Courier key never sits in your app’s environment. It is non-blocking, and that cuts both ways. Auth0 does not wait for the Action to finish, so a slow or failing Action never blocks a signup. It also means a failure is invisible unless you look. Auth0’s own logs are where you find it.

Set it up

Create the Action

In the Auth0 Dashboard, go to Actions → Library, select Build Custom, and create an Action on the Post User Registration trigger.

Add the SDK and your key

In the Action editor, open the Dependencies panel in the left sidebar and add @trycourier/courier. Actions install npm packages into the runtime, so the works here exactly as it does on your own server.Then open the key icon in the same sidebar and add a secret named COURIER_API_KEY with your Courier key as its value.Auth0 exposes the secret to the Action as event.secrets.COURIER_API_KEY. It is never in your application’s environment and never in the Action’s source.

Write the Action

The Action receives the newly created user on event.user. Create the profile, then send.

Post User Registration

const Courier = require("@trycourier/courier");

exports.onExecutePostUserRegistration = async (event) => {
  const courier = new Courier({ apiKey: event.secrets.COURIER_API_KEY });
  const { user_id, email, given_name } = event.user;

  // Auth0's user_id becomes the Courier user id, so both systems agree.
  await courier.profiles.create(user_id, {
    profile: { email, given_name },
  });

  await courier.send.message({
    message: {
      to: { user_id },
      template: "nt_01kx4h2jdafq8bk9aftxak4b40",
      data: { name: given_name ?? "there" },
    },
  });
};

Actions are CommonJS, so the SDK comes in with require rather than import. Everything else is the same code you would write on your own server, and the applies unchanged.

Auth0 does not wait for this Action, so a failed send does not fail the signup and does not surface to the user. Wrap the calls in try/catch and console.log the error, then read it in Monitoring → Logs. Without that, a broken welcome email is silent.

Deploy and add it to the flow

Select Deploy, then go to Actions → Triggers → post-user-registration and drag the Action into the flow between Start and Complete. An Action that is deployed but not in the flow never runs, which is the most common reason nothing happens.

Verify

Create a user through your app’s signup, or from User Management → Users in the Auth0 Dashboard. The trigger fires for Database and Passwordless connections.

Check the Auth0 log

In Monitoring → Logs, find the registration event. A failing Action shows up here and nowhere else.

Confirm the send

Open in Courier and confirm the message.

The trigger fires for Database and Passwordless connections only. A user arriving through a social or enterprise connection does not fire it, so a Google sign-up sends nothing. For those, use a post-login Action and check whether the login is the user’s first.

Adapt it for other triggers

Auth0 trigger	What to send
`post-user-registration`	Welcome, for database and passwordless signups
`post-login`	A new-device or new-location alert
`send-phone-message`	Route Auth0’s own MFA codes through Courier
`post-change-password`	A password-changed confirmation

post-login runs on every login, so gate anything you send there on a condition. Sending on each login is how a welcome email becomes a complaint.

Get started

Send your first message

Build a notification

Send to many people

Send when something happens

Let users choose

Go live

Move to Courier

Send a welcome email from Auth0

What you will build

Prerequisites

How this differs from a webhook

Set it up

Verify

Adapt it for other triggers

​What you will build

​Prerequisites

​How this differs from a webhook

​Set it up

​Verify

​Adapt it for other triggers

What you will build

Prerequisites

How this differs from a webhook

Set it up

Verify

Adapt it for other triggers