Send Emails with Firebase Cloud Functions Using Keplars

Firebase makes it easy to build and scale applications. From authentication and databases to serverless functions, it provides everything developers need to ship products quickly.

However, when it comes to sending transactional emails such as verification emails, welcome messages, password resets, notifications, and newsletters, developers often need a reliable email delivery solution.

That's where Keplars comes in.

With the Keplars Firebase Cloud Functions integration, you can deploy a production-ready email endpoint inside your Firebase project and start sending emails in minutes.

Why Use Keplars with Firebase?

The integration provides:

• Template-based emails
• HTML and plain-text emails
• Scheduled email delivery
• Instant email delivery (0-5 seconds)
• TypeScript support
• Node.js 18 support
• Firebase-native deployment

Whether you're building a SaaS platform, e-commerce store, mobile application, or internal business tool, Keplars helps you send emails directly from your Firebase environment.

Quick Setup

1. Clone the Example Repository

1git clone https://github.com/KeplarsHQ/firebase-cloud-functions-example.git
2
3cd firebase-cloud-functions-example

2. Configure Your Firebase Project

Update your `.firebaserc` file:

1{
2  "projects": {
3    "default": "your-firebase-project-id"
4  }
5}

Or connect your project using:

1firebase use --add

3. Add Your Keplars API Key

Navigate to the functions directory:

1cd functions
2
3cp .env.example .env

Add your API key:

1KEPLARS_API_KEY=kms_your_actual_api_key_here

4. Install Dependencies

1npm install
2
3cd ..

5. Start Firebase Emulator

1firebase emulators:start

Your email endpoint will be available at:

1http://127.0.0.1:5001/your-project-id/us-central1/keplarsEmail

Sending Your First Email

Once your Cloud Function is running, you can send emails using a simple HTTP request.

Template-Based Email

1{
2  "to": ["[email protected]"],
3  "template_id": "your_template_id",
4  "params": {
5    "user_name": "John Doe",
6    "verification_code": "123456"
7  },
8  "delivery_type": "instant"
9}

This approach is ideal for:

• Welcome emails
• OTP verification
• Password resets
• Transactional notifications

Plain Text Emails

1{
2  "to": ["[email protected]"],
3  "subject": "Welcome!",
4  "body": "Thanks for signing up. We're excited to have you.",
5  "delivery_type": "instant"
6}

HTML Emails

Need complete control over email design?

1{
2  "to": ["[email protected]"],
3  "subject": "Welcome!",
4  "html": "<h1>Welcome!</h1><p>Thanks for signing up.</p>",
5  "is_html": true,
6  "delivery_type": "instant"
7}

This is perfect for:

• Marketing campaigns
• Product announcements
• Rich onboarding emails

Scheduled Emails

Keplars also supports scheduled delivery with timezone awareness.

1{
2  "to": ["[email protected]"],
3  "subject": "Weekly Newsletter",
4  "html": "<h1>This Week's Updates</h1>",
5  "scheduled_at": "2026-01-25T10:00:00",
6  "timezone": "America/New_York"
7}

Common use cases include:

• Newsletters
• Product launches
• Reminder emails
• Time-sensitive campaigns

Calling the Function from JavaScript

Once deployed, sending emails from your frontend or backend is straightforward.

1const response = await fetch(
2  'https://us-central1-your-project-id.cloudfunctions.net/keplarsEmail',
3  {
4    method: 'POST',
5    headers: {
6      'Content-Type': 'application/json',
7    },
8    body: JSON.stringify({
9      to: ['[email protected]'],
10      template_id: 'your_template_id',
11      params: {
12        user_name: 'John',
13        verification_code: '123456'
14      },
15      delivery_type: 'instant'
16    })
17  }
18);
19
20const data = await response.json();
21
22console.log('Email sent!', data);

React Integration Example

For React applications, you can trigger emails like this:

1function WelcomeEmail() {
2  const sendWelcome = async (email: string, name: string) => {
3    await fetch(
4      'https://us-central1-your-project-id.cloudfunctions.net/keplarsEmail',
5      {
6        method: 'POST',
7        headers: {'Content-Type': 'application/json'},
8        body: JSON.stringify({
9          to: [email],
10          template_id: 'your_welcome_template_id',
11          params: {user_name: name}
12        })
13      }
14    );
15  };
16
17  return (
18    <button onClick={() => sendWelcome('[email protected]', 'Jane')}>
19      Send Welcome Email
20    </button>
21  );
22}

Deploying to Production

Before deploying, store your API key securely:

1firebase functions:secrets:set KEPLARS_API_KEY

Deploy your Cloud Functions:

1firebase deploy --only functions

Your endpoint will be available at:

1https://us-central1-your-project-id.cloudfunctions.net/keplarsEmail

Security Best Practices

For production deployments, we recommend the following.

Restrict CORS

1res.set(
2  "Access-Control-Allow-Origin",
3  "https://yourdomain.com"
4);

Add Firebase Authentication

1import * as admin from "firebase-admin";
2
3const token =
4  req.headers.authorization?.split("Bearer ")[1];
5
6const decodedToken =
7  await admin.auth().verifyIdToken(token);

Protect Secrets

Never commit API keys to Git. Use Firebase Secrets Manager:

1firebase functions:secrets:set KEPLARS_API_KEY

Email Delivery Response

A successful API response returns the following delivery information.

1{
2  "id": "msg_...",
3  "object": "email",
4  "status": "queued",
5  "created_at": "2026-01-22T22:14:04.470Z"
6}

This makes it easy to track email activity inside your application.

Final Thoughts

Firebase simplifies backend infrastructure. Keplars simplifies email infrastructure.

Together, they provide a powerful solution for developers who need reliable transactional and scheduled email delivery without maintaining complex mail servers.

If you're already using Firebase Cloud Functions, integrating Keplars takes only a few minutes and gives your application access to scalable, production-ready email delivery.

Useful Links:

• Firebase Integration Docs
• Keplars Platform
• Documentation