resend

What this skill does

# Resend

## Overview

Resend is a modern email API built for developers, providing programmatic email sending with support for React Email components, domain management, and webhook-driven event tracking.

**When to use:** Transactional emails (welcome, password reset, receipts), batch email delivery, scheduled sending, webhook-based delivery tracking, domain verification, React Email integration.

**When NOT to use:** High-volume marketing automation (use dedicated ESP), SMS/push notifications, email hosting/inbox management.

## Quick Reference

| Pattern          | API                                         | Key Points                                                    |
| ---------------- | ------------------------------------------- | ------------------------------------------------------------- |
| Send email       | `resend.emails.send({ from, to, subject })` | Returns `{ data, error }`, supports html/text/react content   |
| Send with React  | `resend.emails.send({ react: <Email /> })`  | Node.js SDK only, renders React Email components server-side  |
| Batch send       | `resend.batch.send([...emails])`            | Multiple emails in one request, no attachments/scheduling     |
| Schedule email   | `emails.send({ scheduled_at })`             | ISO 8601 or natural language, cancel before send window       |
| Attachments      | `emails.send({ attachments: [...] })`       | Max 40MB total after encoding, supports content or path       |
| Idempotent send  | `emails.send(params, { idempotencyKey })`   | Prevents duplicate sends on retry                             |
| Retrieve email   | `resend.emails.get(emailId)`                | Check delivery status and metadata                            |
| Add domain       | `resend.domains.create({ name })`           | Returns DNS records for SPF, DKIM, MX                         |
| Verify domain    | `resend.domains.verify(domainId)`           | Triggers DNS record check                                     |
| List domains     | `resend.domains.list()`                     | Returns all domains with status                               |
| Create webhook   | Dashboard or API                            | Subscribe to email lifecycle events                           |
| Verify webhook   | `resend.webhooks.verify({ payload, ... })`  | Validates Svix signature headers                              |
| Tags             | `emails.send({ tags: [...] })`              | Key-value pairs for categorization, ASCII only, max 256 chars |
| Custom headers   | `emails.send({ headers: {...} })`           | Add custom email headers                                      |
| Create contact   | `resend.contacts.create({ email, ... })`    | Global contacts with custom properties                        |
| List contacts    | `resend.contacts.list()`                    | Returns all contacts                                          |
| Create broadcast | `resend.broadcasts.create({ from, ... })`   | Bulk email to a segment, supports template variables          |
| Send broadcast   | `resend.broadcasts.send(id, { segmentId })` | Delivers broadcast to a segment of contacts                   |

## Common Mistakes

| Mistake                                    | Correct Pattern                                                      |
| ------------------------------------------ | -------------------------------------------------------------------- |
| Using root domain for sending              | Use a subdomain like `send.yourdomain.com` to isolate reputation     |
| Not checking `error` in response           | Always destructure `{ data, error }` and handle errors               |
| Sending attachments in batch requests      | Attachments and scheduling are not supported in batch sends          |
| Hardcoding API key in source code          | Use environment variable `RESEND_API_KEY`                            |
| Skipping webhook signature verification    | Always verify using Svix headers before processing events            |
| Using `react` prop outside Node.js SDK     | The `react` prop only works with the Node.js SDK                     |
| Not setting up DMARC after SPF/DKIM verify | Add DMARC record after SPF and DKIM pass to improve deliverability   |
| Exceeding 50 recipients in a single send   | Use batch send or loop for more than 50 recipients per request       |
| Using `&&` for tag name/value characters   | Tag names and values must be ASCII letters, numbers, `_`, or `-`     |
| Ignoring bounce/complaint webhooks         | Monitor `email.bounced` and `email.complained` to protect reputation |

## Delegation

- **Email template design**: Use `Explore` agent to discover React Email component patterns
- **Domain DNS configuration**: Use `Task` agent for step-by-step DNS setup verification
- **Webhook endpoint setup**: Use `Task` agent for route handler implementation

## References

- [Sending emails, batch sending, attachments, scheduling, and idempotency](references/sending-emails.md)
- [Contacts, Segments, Broadcasts, template variables, and bulk sending](references/contacts-and-broadcasts.md)
- [Domain verification, DNS records, and sender identity management](references/domain-management.md)
- [Webhook events, signature verification, and event handling](references/webhooks.md)