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.