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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 <onboarding@resend.dev>',
    to: ['delivered@resend.dev'],
    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 <onboarding@resend.dev>",
    "to": ["delivered@resend.dev"],
    "subject": "Hello World",
    "html": "<p>Email body here</p>",
}, idempotency_key=f"welcome-email/{user_id}")

Single vs Batch Decision

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 });
}

Key gotcha: Webhook payloads do NOT contain the email body. You must call resend.emails.receiving.get() separately.

What Do You Need?

SDK Version Requirements

Always install the latest SDK version. These are the minimum versions for full functionality (sending, receiving, webhook verification):

If the project already has a Resend SDK installed , check the version and upgrade if it's below the minimum. Older SDKs may be missing webhooks.verify() or emails.receiving.get().

See installation.md for full installation commands, language detection, and cURL fallback.

Common Setup

API Key

Store in environment variable — never hardcode:

export RESEND_API_KEY=re_xxxxxxxxx

Get your key at resend.com/api-keys.

Detect Project Language

Check for these files: package.json (Node.js), requirements.txt/pyproject.toml (Python), go.mod (Go), Gemfile (Ruby), composer.json (PHP), Cargo.toml (Rust), pom.xml/build.gradle (Java), *.csproj (.NET).

Common Mistakes

| Mistake | Fix

---|---|---
1 | Retrying without idempotency key | Always include idempotency key — prevents duplicate sends on retry. Format: <event-type>/<entity-id>
2 | Not verifying webhook signatures | Always verify with resend.webhooks.verify() — unverified events can't be trusted
3 | Template variable name mismatch | Variable names are case-sensitive — must match the template definition exactly. Use triple mustache {{{VAR}}} syntax
4 | Expecting email body in webhook payload | Webhooks contain metadata only — call resend.emails.receiving.get() for body content
5 | Using try/catch for Node.js SDK errors | SDK returns { data, error } — check error explicitly, don't wrap in try/catch
6 | Using batch for emails with attachments | Batch doesn't support attachments — use single sends instead
7 | Testing with fake emails (test@gmail.com) | Use — fake addresses bounce and hurt reputation 8 | | Templates must be published before sending — call first 9 | | Mutually exclusive — remove // when using template 10 | | Ensure Resend's MX has the lowest number (highest priority) or emails won't route

Cross-Cutting Concerns

Send + Receive Together

Auto-replies, email forwarding, or any receive-then-send workflow requires both capabilities:

1. Set up inbound domain first (see receiving.md)
2. Set up sending (see sending/overview.md)
3. Note: batch sending does NOT support attachments or scheduling — use single sends when forwarding with attachments

AI Agent Inbox

If your system processes untrusted email content and takes actions (refunds, database changes, forwarding), install the agent-email-inbox skill. This applies whether or not AI is involved — any system interpreting freeform email content from external senders needs security measures.

Marketing Emails

The sending capabilities in this skill are for transactional email (receipts, confirmations, notifications). For marketing campaigns to large subscriber lists with unsubscribe links and engagement tracking, use Resend Broadcasts.

Domain Warm-up

New domains must gradually increase sending volume. Day 1 limit: ~150 emails (new domain) or ~1,000 (existing domain). See the warm-up schedule in sending/overview.md.

Testing

Never test with fake addresses at real email providers (test@gmail.com, fake@outlook.com) — they bounce and destroy sender reputation.

Suppression List

Resend automatically suppresses hard-bounced and spam-complained addresses. Sending to suppressed addresses fires the email.suppressed webhook event instead of attempting delivery. Manage in Dashboard → Suppressions.

Webhook Event Types

See webhooks.md for full details, signature verification, and retry schedule.

Error Handling Quick Reference

Resources

• Resend Documentation
• API Reference
• Dashboard

Weekly Installs

4.1K

Repository

resend/resend-skills

GitHub Stars

91

First Seen

Jan 28, 2026

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