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 `RESENDAPIKEY`
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)

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