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SMTP

Nodemailer

Use Nodemailer to send email through the Lettermint SMTP relay from Node.js.

Installation

Install nodemailer via your package manager:

Basic configuration

Use environment variables for credentials:

Code
const SMTP_HOST = 'smtp.lettermint.co';
const SMTP_USERNAME = 'lettermint';
const API_TOKEN = process.env.LETTERMINT_PROJECT_TOKEN;

Advanced features

Multiple recipients

Code
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>',
};

Attachments

Code
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' }),
    },
  ],
};

Custom headers

Code
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',
  },
};

Metadata for tracking

Add metadata that will be included in webhook payloads:

Code
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',
  },
};

Lettermint headers

Add Lettermint-specific headers for tags, metadata, and routing:

Code
const mailOptions = {
  from: 'sender@yourdomain.com',
  to: 'recipient@example.com',
  subject: 'Order Confirmation',
  html: '<p>Your order has been confirmed.</p>',
  headers: [
    // Existing singular tag
    { key: 'X-LM-Tag', value: 'order-confirmation' },
    // Structured tags. Nodemailer supports repeated custom headers.
    { key: 'X-LM-Tags', value: 'campaign=orders, environment=production' },
    { key: 'X-LM-Tags', value: 'variant=B' },
    // Metadata for tracking (included in webhooks)
    { key: 'X-LM-Metadata-order_id', value: '12345' },
    { key: 'X-LM-Metadata-customer_id', value: 'cust_789' },
    // Route selection
    { key: 'X-Lettermint-Route', value: 'transactional' },
  ],
};

X-LM-Tag is the singular tag. X-LM-Tags contains structured pairs. Nodemailer writes each array item as a separate custom header.