Resend JS SDK and Custom Headers Cheat Sheet

This quick reference guide summarizes the most common patterns and configurations in Resend using the official Node.js SDK.

1. SDK Client Initialization

import { Resend } from "resend";

// Initialize the API client
const resend = new Resend("re_your-secret-key");

2. Dispatching a Single Email

await resend.emails.send({
  from: "Support Team <support@mycompany.com>",
  to: ["customer@gmail.com"],
  subject: "Updates on your order",
  html: "<p>Your order has shipped!</p>",
  // Optional custom mail headers configuration
  headers: {
    "X-Entity-Ref-ID": "order-12345",
  },
  attachments: [
    {
      filename: "invoice.pdf",
      content: "Invoice document content string",
    },
  ],
});

3. Dispatching Emails in Batches (Maximum 100 per request)

await resend.batch.send([
  {
    from: "Mailing List <news@mycompany.com>",
    to: ["recipient_a@gmail.com"],
    subject: "Newsletter Issue 1",
    html: "<p>Read details inside</p>",
  },
  {
    from: "Mailing List <news@mycompany.com>",
    to: ["recipient_b@gmail.com"],
    subject: "Newsletter Issue 1",
    html: "<p>Read details inside</p>",
  },
]);

4. Common Error Codes Reference