Email Patterns with Resend and React Email

Quick Guide: Use Resend for transactional emails with React Email templates. Always await render() before sending (it returns a Promise). Server-side only - never expose API keys to clients. Implement retry with exponential backoff for transient failures. Include unsubscribe links in non-transactional emails (CAN-SPAM). Use resend.batch.send() for 2-100 recipients (no attachments or scheduling support in batch). React Email 5.0+ deprecated renderAsync - use render() instead. Webhook verification requires raw request body and webhookSecret parameter.

<critical_requirements>

CRITICAL: Before Using This Skill

All code must follow project conventions in CLAUDE.md (kebab-case, named exports, import ordering, import type, named constants)

(You MUST await render() before passing HTML to resend.emails.send() - render returns a Promise)

(You MUST handle Resend API errors and implement retry logic for transient failures)

(You MUST use server-side sending for all emails - never expose RESEND_API_KEY to the client)

(You MUST include unsubscribe links in marketing/notification emails - required for CAN-SPAM compliance)