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Node.js

The official Lettermint Node.js SDK sends email through a small, fully typed fluent API. You chain the parts of a message and call send(), and because the request and response types ship with the package, every field autocompletes in your editor. It runs anywhere Node runs: API routes, background workers, queue consumers, and serverless functions.

Every message is delivered through Lettermint's European infrastructure, which runs entirely inside the EU and processes mail in line with GDPR. That makes the SDK a solid choice for transactional email from a Node app, such as order confirmations, password resets, and account notifications.

Requirements

Before you start you need:

• Node.js 18 or newer
• A Lettermint account with a verified sending domain
• A Project API token from your project settings

If your domain is not verified yet, follow the domain setup guide first so your mail reaches the inbox instead of the spam folder.

1. Installation

Install the SDK via your preferred package manager:

2. Send your first email

Initialize the email client with your Project API token:

Code
import { Lettermint } from "lettermint";

const email = Lettermint.email(process.env.LETTERMINT_PROJECT_TOKEN!);

Send your first email:

Code
const response = await email
  .from('John Doe <john@yourdomain.com>')
  .to('recipient@example.com')
  .subject('Hello from Lettermint')
  .text('This is a test email sent using the Lettermint Node.js SDK.')
  .send();

console.log(`Email sent with ID: ${response.message_id}`);

3. Email Features

Basic Email

Send a simple text or HTML email:

Code
const response = await email
    .from('John Doe <john@yourdomain.com>')
    .to('recipient@example.com')
    .subject('Your account is ready!')
    .html('<h1>Welcome!</h1><p>Thanks for signing up.</p>')
    .text('Welcome! Thanks for signing up.')
    .send();

Multiple Recipients

Send to multiple recipients using CC and BCC:

Code
const response = await email
    .from('John Doe <john@yourdomain.com>')
    .to('user1@example.com', 'user2@example.com')
    .cc('manager@yourdomain.com')
    .bcc('archive@yourdomain.com')
    .subject('Monthly Newsletter')
    .html('<h1>This Month\'s Updates</h1>')
    .send();

Custom Headers and Reply-To

Add custom headers and set reply-to addresses:

Code
const response = await email
    .from('support@yourdomain.com')
    .to('customer@example.com')
    .replyTo('help@yourdomain.com')
    .subject('Support Ticket #12345')
    .headers({
        'X-Priority': '1',
        'X-Ticket-ID': '12345'
    })
    .html('<p>Your support ticket has been updated.</p>')
    .send();

Metadata

Add metadata for tracking and webhook payloads:

Code
const response = await email
    .from('notifications@yourdomain.com')
    .to('user@example.com')
    .subject('Order Confirmation')
    .metadata({
        'order_id': '12345',
        'customer_id': 'cust_789',
        'campaign': 'order_confirmation'
    })
    .html('<p>Your order has been confirmed.</p>')
    .send();

Tags

Categorize emails for filtering and analytics:

Code
const response = await email
    .from('alerts@yourdomain.com')
    .to('admin@example.com')
    .subject('System Alert')
    .tag('system-alerts')
    .html('<p>Critical system alert detected.</p>')
    .send();

Route Selection

Direct emails to specific routes within your project:

Code
const response = await email
    .from('notifications@yourdomain.com')
    .to('user@example.com')
    .subject('Welcome!')
    .route('transactional')
    .html('<p>Welcome to our platform.</p>')
    .send();

Idempotency

Pass an idempotency key so a retry never sends the same email twice. If a request with the same key is repeated within the idempotency window, Lettermint returns the original result instead of sending again:

Code
const response = await email
    .from('notifications@yourdomain.com')
    .to('user@example.com')
    .subject('Order Confirmation')
    .idempotencyKey('order-confirmation-12345')
    .html('<p>Your order has been confirmed.</p>')
    .send();

File Attachments

Attach files to your emails:

Code
import fs from 'fs';

// Read file content
const fileContent = fs.readFileSync('/path/to/document.pdf');
const base64Content = fileContent.toString('base64');

const response = await email
    .from('invoices@yourdomain.com')
    .to('customer@example.com')
    .subject('Your Invoice')
    .html('<p>Please find your invoice attached.</p>')
    .attach('invoice.pdf', base64Content)
    .send();

4. Send an order confirmation

A real transactional send usually pulls several of these features together. This example sends a receipt with an HTML and plain-text body, tags it for analytics, attaches the order and customer IDs as metadata, and uses an idempotency key so a retry never emails the customer twice:

Code
import { Lettermint } from "lettermint";

const email = Lettermint.email(process.env.LETTERMINT_PROJECT_TOKEN!);

interface Order {
  id: string;
  number: string;
  total: string;
  customerEmail: string;
  customerId: string;
}

export async function sendOrderConfirmation(order: Order) {
  return await email
    .from('Acme Store <orders@yourdomain.com>')
    .to(order.customerEmail)
    .replyTo('support@yourdomain.com')
    .subject(`Order ${order.number} confirmed`)
    .html(`<h1>Thanks for your order</h1><p>Order ${order.number} totalling ${order.total} is confirmed.</p>`)
    .text(`Thanks for your order. Order ${order.number} totalling ${order.total} is confirmed.`)
    .tag('order-confirmation')
    .metadata({ order_id: order.id, customer_id: order.customerId })
    .idempotencyKey(`order-confirmation-${order.id}`)
    .route('transactional')
    .send();
}

The metadata you attach here travels with every webhook event for the message, so a later delivery or bounce maps straight back to the order in your database.

5. Response

Code
const response = await email
    .from('John Doe <john@yourdomain.com>')
    .to('recipient@example.com')
    .subject('Test')
    .text('Hello!')
    .send();

console.log(`Email sent with ID: ${response.message_id}`);
console.log(`Status: ${response.status}`);

Track delivery, opens, and bounces

Sending is only half of a transactional setup. To see what happens after a message leaves your app, combine the SDK with Lettermint's platform features:

• Email tracking records opens and clicks, with bot filtering so your metrics stay accurate.
• Webhooks push delivery, bounce, and complaint events to your server in real time, so you can update order records or suppress bad addresses.
• Test addresses let you trigger a hard or soft bounce on demand while you build and verify your webhook handler.

Tracking is configured per route, so turn it on for the route your app sends through, then read the results from your dashboard or your webhook endpoint.

FAQ

Does the SDK support TypeScript?

Yes. The SDK is written in TypeScript and exports its request and response types, so every builder method and field is typed and autocompletes in your editor.

How do I stop the same email being sent twice?

Add an idempotency key with .idempotencyKey(), derived from a stable ID such as an order number. A repeated request with the same key returns the original result instead of sending again. See the idempotency documentation.

Is Lettermint email GDPR compliant and EU-hosted?

Yes. Lettermint runs exclusively on European infrastructure and processes email in line with GDPR, so transactional mail from your Node app is handled inside the EU.

How do I track opens, clicks, and bounces?

Enable tracking on your route and subscribe to webhooks to receive delivery, open, and bounce events. Use the test addresses to simulate bounces while you build your handler.

Next Steps