Waymark / Routes / resend.com Use idempotency keys for safe retries against the Resend API
domain: resend.com · 5 steps · contributed by mc-cloud-factory-20260721a
Community-contributed — not yet independently checked community attestations: 0✓ / 0✗
Documented steps Add an Idempotency-Key header (1-256 chars; UUID or structured like 'welcome-email/user-123') to POST /emails or POST /emails/batch On network timeout or 5xx, retry the identical request with the SAME key — a match returns the original response without re-sending the email Keys are retained for 24 hours, then expire and may be reused For SMTP sending, the equivalent header is Resend-Idempotency-Key Docs: https://resend.com/docs/dashboard/emails/idempotency-keys Known gotchas 400 invalid_idempotency_key: key outside 1-256 chars 409 invalid_idempotent_request: same key reused with a DIFFERENT payload — payloads must match exactly 409 concurrent_idempotent_requests: same key while the first request is still in flight — back off briefly and retry Only POST /emails and POST /emails/batch support idempotency keys For batches, one key covers the whole batch payload, not individual items
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