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This guide covers SMTP integration. For full configuration options and available headers, see the SMTP Introduction.

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Installation

Install nodemailer via your package manager: 
npm install nodemailer

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Basic Configuration

Use environment variables for credentials: 
const SMTP_HOST = 'smtp.lettermint.co';
const SMTP_USERNAME = 'lettermint';
const API_TOKEN = process.env.LETTERMINT_API_TOKEN;

const nodemailer = require('nodemailer');

const transporter = nodemailer.createTransport({
  host: 'smtp.lettermint.co',
  port: 587,
  secure: false, // STARTTLS
  auth: {
    user: 'lettermint',
    pass: process.env.LETTERMINT_API_TOKEN,
  },
});

async function sendEmail() {
  try {
    const info = await transporter.sendMail({
      from: 'sender@yourdomain.com',
      to: 'recipient@example.com',
      subject: 'Test Email',
      text: 'Hello! This is a test email.',
      html: '<h1>Hello!</h1><p>This is a test email.</p>',
    });

    console.log('Message sent:', info.messageId);
  } catch (error) {
    console.error('Error sending email:', error);
  }
}

sendEmail();

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Advanced Features

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Multiple Recipients

const mailOptions = {
  from: 'sender@yourdomain.com',
  to: ['user1@example.com', 'user2@example.com'],
  cc: 'manager@yourdomain.com',
  bcc: 'archive@yourdomain.com',
  subject: 'Newsletter',
  html: '<h1>Monthly Update</h1>',
};

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Attachments

const mailOptions = {
  from: 'sender@yourdomain.com',
  to: 'recipient@example.com',
  subject: 'Document Attached',
  html: '<p>Please find the document attached.</p>',
  attachments: [
    {
      filename: 'document.pdf',
      path: './files/document.pdf',
    },
    {
      filename: 'data.json',
      content: JSON.stringify({ key: 'value' }),
    },
  ],
};

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Custom Headers

const mailOptions = {
  from: 'sender@yourdomain.com',
  to: 'recipient@example.com',
  subject: 'Custom Headers',
  html: '<p>Email with custom headers.</p>',
  headers: {
    'X-Priority': '1',
    'X-Custom-Header': 'Custom Value',
  },
};

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Metadata for Tracking

Add metadata that will be included in webhook payloads: 
const mailOptions = {
  from: 'sender@yourdomain.com',
  to: 'recipient@example.com',
  subject: 'Order Confirmation',
  html: '<p>Your order has been confirmed.</p>',
  headers: {
    'X-LM-Metadata-order_id': '12345',
    'X-LM-Metadata-customer_id': 'cust_789',
    'X-LM-Metadata-campaign': 'order_confirmation',
  },
};

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Lettermint Headers

Add Lettermint-specific headers for tags, metadata, and routing: 
const mailOptions = {
  from: 'sender@yourdomain.com',
  to: 'recipient@example.com',
  subject: 'Order Confirmation',
  html: '<p>Your order has been confirmed.</p>',
  headers: {
    // Tag for categorization
    'X-LM-Tag': 'order-confirmation',
    // Metadata for tracking (included in webhooks)
    'X-LM-Metadata-order_id': '12345',
    'X-LM-Metadata-customer_id': 'cust_789',
    // Route selection
    'X-Lettermint-Route': 'transactional',
  },
};
Metadata headers are extracted by Lettermint and included in webhook payloads, but not added to the actual email sent to recipients. See the SMTP Introduction for full details on available headers.