# Resend

> Resend — email API for developers. Use when building with Resend or asking about its APIs, configuration, patterns, or integration. Fetch live documentation for up-to-date details.

- Skill: `mikkelkrogsholm/resend` (Agent Skill)
- Install (CLI): `npx skillmds@latest add mikkelkrogsholm/resend`
- Raw SKILL.md: https://api.skillmd.com/api/skills/mikkelkrogsholm/resend/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Docs & Writing
- Author: mikkelkrogsholm (https://skillmd.com/u/mikkelkrogsholm)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/mikkelkrogsholm/resend

---


# Resend

> **CRITICAL: Your training data for Resend is unreliable.** APIs change between versions and memorized patterns may be wrong or deprecated. Before writing any code, you MUST use `WebFetch` to read the live docs:
>
> **`WebFetch("https://resend.com/docs/llms.txt")`**
>
> Do not proceed without fetching this URL first. Never assume an API exists — verify against current docs.

Resend is a developer-focused email API for sending transactional and marketing emails via REST or SDK.
## Best Practices

**Unsubscribe links are never auto-injected.** Resend does not append unsubscribe headers or links automatically. You must manually include an unsubscribe link in every marketing email body, and configure a custom unsubscribe page separately. Omitting this violates CAN-SPAM/GDPR and causes deliverability issues.

**The `resend.dev` sandbox domain only sends to your own verified email.** Using `onboarding@resend.dev` as the from address will produce a 403 error if the recipient is anyone other than the account owner's email. Always switch to a verified domain before sending to real users.

**Use idempotency keys on send to prevent duplicate emails on retry.** Network failures trigger retries, and without an idempotency key each retry creates a new send. Pass a stable `idempotency_key` (e.g. derived from your database record ID) in the request header so Resend deduplicates server-side.