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 }

error

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

POST /emails

POST /emails/batch

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:

<event-type>/<entity-id>

welcome-email/user-123

batch-<event-type>/<batch-id>

batch-orders/batch-456

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()

What Do You Need?

agent-email-inbox

SDK Version Requirements

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

resend

npm install resend

resend

pip install resend

resend-go/v3

go get github.com/resend/resend-go/v3

resend

gem install resend

resend/resend-php

composer require resend/resend-php

resend-rs

cargo add resend-rs

resend-java

Resend

dotnet add package Resend

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

requirements.txt

pyproject.toml

go.mod

Gemfile

composer.json

Cargo.toml

pom.xml

build.gradle

*.csproj

Common Mistakes

<event-type>/<entity-id>

resend.webhooks.verify()

{{{VAR}}}

resend.emails.receiving.get()

{ data, error }

error

delivered@resend.dev

.publish()

html

template

html

text

react

resend.dev

onboarding@resend.dev

from

send.acme.com

user@acme.com

restricted_api_key

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

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 — see broadcasts.md for the API.

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.

delivered@resend.dev

bounced@resend.dev

complained@resend.dev

Suppression List

Resend automatically suppresses hard-bounced and spam-complained addresses. Sending to suppressed addresses fires the

email.suppressed

Webhook Event Types

email.sent

email.delivered

email.bounced

email.complained

email.opened

email.clicked

email.delivery_delayed

email.received

domain.*

contact.*

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

Error Handling Quick Reference

restricted_api_key

resend.dev

from

Resources

• Resend Documentation
• API Reference
• Dashboard