email-users

Firebase SDK for Cloud Functions Quickstart - Auth triggers

This quickstart demonstrates how to setup an Auth triggered Cloud Function using the Firebase SDK for Cloud Functions and Resend.

Introduction

We'll deploy 2nd gen Auth triggered functions that send a welcome email when a new user signs up and a goodbye email when user accounts are deleted.

• Read more about Cloud Functions for Firebase
• Read more about the Firebase Local Emulator Suite
• Connect Cloud Functions to the Emulator

Functions Code

The functions are organized into separate files for clean, self-contained documentation snippets and modular code:

• functions/sendWelcomeEmail.js: sendWelcomeEmail triggers on all user creations across the project (default behavior).
• functions/sendByeEmail.js: sendByeEmail triggers when any user account is deleted.
• functions/tenants.js: Multi-tenancy examples:
  • sendWelcomeEmailToTenant: Scoped to users in a specific Identity Platform tenant using tenantId: "my-tenant-id".
  • sendWelcomeEmailNoTenant: Triggers only for users not associated with any tenant using tenantId: IS_NOT_TENANT.
• functions/utils/myEmailService.js: Configures the Resend client, defines the EMAIL_API_KEY secret, and provides the sendEmail, sendWelcomeEmail, and sendGoodbyeEmail helpers.
• functions/index.js: Entry point re-exporting all function triggers.

Sending emails is performed using Resend. The dependencies are listed in functions/package.json.

Set up the sample

1. Clone or download this repo and navigate to Node/quickstarts/email-users:

   cd Node/quickstarts/email-users

2. Install Cloud Functions dependencies:

   cd functions && pnpm install && cd ..

3. Set your Resend API key for local development in functions/.secret.local (the emulator reads secret values from that file):

   EMAIL_API_KEY="re_123456789"

   You can obtain a free API key from Resend.

Run locally with the Firebase Emulator Suite

The Firebase Local Emulator Suite lets you test Auth triggers and create/delete users directly in the Emulator UI without deploying to a live project.

1. Start the emulators:

   firebase emulators:start

2. Open the Emulator Suite UI in your browser at http://localhost:4000 (or the port printed in your terminal).
3. Navigate to the Authentication tab.
4. Trigger sendWelcomeEmail: Click Add user, enter an email address and display name, and click Save.
5. Trigger sendByeEmail: Select the user you just created and click Delete user.
6. View the logs in the Logs tab of the Emulator Suite UI or in your terminal to see the functions execute:

   New welcome email sent to: user@example.com
Account deletion confirmation email sent to: user@example.com

Deploy to production

To deploy the functions to a live Firebase project:

1. Configure your Firebase project:

   firebase use --add

2. Set your Resend API key as a Cloud Secret:

   firebase functions:secrets:set EMAIL_API_KEY

3. Deploy the functions:

   firebase deploy --only functions

Contributing

We'd love that you contribute to the project. Before doing so please read our Contributor guide.

License

© Google, 2026. Licensed under an Apache-2 license.