resend

Resend

Quick Send — Node.js

import { Resend } from 'resend';

const resend = new Resend(process.env.RESEND_API_KEY);

const { data, error } = await resend.emails.send(
  {
    from: 'Acme <[email protected]>',
    to: ['[email protected]'],
    subject: 'Hello World',
    html: '<p>Email body here</p>',
  },
  { idempotencyKey: `welcome-email/${userId}` }
);

if (error) {
  console.error('Failed:', error.message);
  return;
}
console.log('Sent:', data.id);

Key gotcha: The Resend Node.js SDK does NOT throw exceptions — it returns { data, error }. Always check error explicitly instead of using try/catch for API errors.

Quick Send — Python

import resend
import os

resend.api_key = os.environ["RESEND_API_KEY"]

email = resend.Emails.send({
    "from": "Acme <[email protected]>",
    "to": ["[email protected]"],
    "subject": "Hello World",
    "html": "<p>Email body here</p>",
}, idempotency_key=f"welcome-email/{user_id}")

Single vs Batch Decision

Choose	When
Single (POST /emails)	1 email, needs attachments, needs scheduling
Batch (POST /emails/batch)	2-100 distinct emails, no attachments, no scheduling

Batch is atomic — if one email fails validation, the entire batch fails. Always validate before sending. Batch does NOT support attachments or scheduled_at.

Idempotency Keys (Critical for Retries)

Prevent duplicate emails when retrying failed requests:

Key Facts
Format (single)	<event-type>/<entity-id> (e.g., welcome-email/user-123)
Format (batch)	batch-<event-type>/<batch-id> (e.g., batch-orders/batch-456)
Expiration	24 hours
Max length	256 characters
Same key + same payload	Returns original response without resending
Same key + different payload	Returns 409 error

Quick Receive (Node.js)

import { Resend } from 'resend';

const resend = new Resend(process.env.RESEND_API_KEY);

export async function POST(req: Request) {
  const payload = await req.text(); // Must use raw text, not req.json()

  const event = resend.webhooks.verify({
    payload,
    headers: {
      'svix-id': req.headers.get('svix-id'),
      'svix-timestamp': req.headers.get('svix-timestamp'),
      'svix-signature': req.headers.get('svix-signature'),
    },
    secret: process.env.RESEND_WEBHOOK_SECRET,
  });

  if (event.type === 'email.received') {
    // Webhook has metadata only — call API for body
    const { data: email } = await resend.emails.receiving.get(
      event.data.email_id
    );
    console.log(email.text);
  }

  return new Response('OK', { status: 200 });
}