resend-api

---
name: resend-api
description: Use when sending transactional or batch emails from Node.js with Resend — including React email templates, attachments, and audiences.
source: https://resend.com/docs
generated: 2026-07-02T18:43:14.331Z
category: api
audience: engineers
---

## When to use

- Sending transactional emails (receipts, password resets, notifications) from a backend
- Rendering email templates with React via react-email
- Sending batch emails or managing contacts and audiences
- Verifying sending domains and handling email webhooks

## Key concepts

### Resend client

Instantiated with `new Resend(apiKey)`. All operations hang off this client: resend.emails, resend.batch, resend.domains, resend.audiences, resend.contacts.

### from address & verified domains

The `from` address must use a domain you've verified in Resend (DKIM/SPF). Unverified domains can only send from the onboarding@resend.dev test sender.

### React email templates

Pass a React component to the `react` field; Resend renders it to HTML server-side. Works with the react-email component library.

### Batch sending

resend.batch.send() accepts an array of up to 100 email objects in one call, each delivered independently.

### Idempotency

Pass an idempotencyKey in the request options to prevent duplicate sends on retries within the idempotency window.

### Webhooks

Resend posts events (email.sent, email.delivered, email.bounced, email.complained, email.opened, email.clicked) signed via Svix headers for verification.

## API reference

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

Create the Resend SDK client with your API key.

```
import { Resend } from 'resend';
const resend = new Resend(process.env.RESEND_API_KEY);
```

```
resend.emails.send({ from, to, subject, html | text | react, ... })
```

Send a single email; returns { data: { id }, error }.

```
const { data, error } = await resend.emails.send({
  from: 'Acme <onboarding@acme.com>',
  to: ['user@example.com'],
  subject: 'Welcome',
  html: '<strong>Hello!</strong>',
});
if (error) console.error(error);
```

```
resend.emails.send({ react: <Component /> })
```

Render a React component to HTML for the email body.

```
import { WelcomeEmail } from './emails/welcome';
await resend.emails.send({
  from: 'Acme <hi@acme.com>',
  to: 'user@example.com',
  subject: 'Welcome',
  react: WelcomeEmail({ name: 'Ada' }),
});
```

```
send with cc, bcc, reply_to, attachments, headers, tags
```

Add CC/BCC recipients, reply-to, file attachments, custom headers, and metadata tags.

```
await resend.emails.send({
  from: 'Acme <hi@acme.com>',
  to: 'user@example.com',
  subject: 'Invoice',
  html: '<p>See attached</p>',
  attachments: [{ filename: 'invoice.pdf', content: pdfBuffer }],
  reply_to: 'support@acme.com',
  tags: [{ name: 'category', value: 'invoice' }],
});
```

```
resend.batch.send([ email1, email2, ... ])
```

Send up to 100 emails in a single request.

```
await resend.batch.send([
  { from: 'a@acme.com', to: 'x@e.com', subject: 'Hi', html: '<p>1</p>' },
  { from: 'a@acme.com', to: 'y@e.com', subject: 'Hi', html: '<p>2</p>' },
]);
```

```
resend.emails.send(payload, { idempotencyKey })
```

Pass options to make a send idempotent across retries.

```
await resend.emails.send(
  { from: 'a@acme.com', to: 'x@e.com', subject: 'Hi', html: '<p>Hi</p>' },
  { idempotencyKey: 'welcome/user_123' }
);
```

```
resend.domains.create/list/verify, resend.audiences, resend.contacts
```

Manage sending domains, marketing audiences, and their contacts via the SDK.

```
await resend.domains.create({ name: 'acme.com' });
await resend.contacts.create({ email: 'user@e.com', audienceId: 'aud_123' });
```

```
resend.emails.get(id) / resend.emails.update / resend.emails.cancel
```

Retrieve a sent email's status, update a scheduled email, or cancel a scheduled send.

```
const { data } = await resend.emails.get('email_id');
await resend.emails.cancel('email_id');
```

## Gotchas

- The `from` domain must be verified in Resend; otherwise sends fail unless you use onboarding@resend.dev for testing.
- The SDK does not throw on API errors — always check the returned `error` field alongside `data`.
- Free/test API keys can only send to your own verified email address until a domain is verified.
- Batch send is capped at 100 emails per request, and batch does not support attachments or scheduled_at.
- Verify webhooks using the Svix signature headers (svix-id, svix-timestamp, svix-signature); don't trust unsigned payloads.
- Attachment content should be a Buffer or base64 string; very large attachments hit per-message size limits.
- Scheduling uses scheduled_at with an ISO 8601 or natural-language time; past times send immediately.
- Rate limits apply per account (default ~2 requests/sec); handle 429 responses with backoff.

---
Generated by SkillMake from https://resend.com/docs on 2026-07-02T18:43:14.331Z.
Verify against source before relying on details.

File: ~/.claude/skills/resend-api/SKILL.md