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
Exploreagent to discover React Email component patterns - Domain DNS configuration: Use
Taskagent for step-by-step DNS setup verification - Webhook endpoint setup: Use
Taskagent for route handler implementation