Idempotency & retries
Safely retry sends without duplicating mail.
Networks fail mid-request. To retry safely, pass an Idempotency-Key header on send requests. If a request with the same key is retried we return the original result instead of sending again.
Use a stable key per logical send
Derive the key from your own event ID (e.g. order ID) so retries reuse the same key and deduplicate. Keys are scoped to your workspace and retained to cover realistic retry windows.
Rate limits
Exceed the limit and you get a 429 with a Retry-After header — back off and retry. For large fan-outs, prefer a campaign or a batch.