resend

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
• Contacts, Segments, Broadcasts, template variables, and bulk sending
• Domain verification, DNS records, and sender identity management
• Webhook events, signature verification, and event handling