Idempotency key
A unique value you send with a request so that retrying it doesn't repeat the action.
How this affects you
Send an Idempotency-Key header with POST /emails and retrying after a timeout becomes safe: the same key with the same body within 24 hours returns the first email's ID and sends nothing. The same key with a different body returns 409 idempotency_conflict. Use something tied to the event, such as order-1042-receipt.
Learn more
Vaartix is a transactional email API built in India. SPF, DKIM and a return path on your domain are set up for you, and every feature is free during the private beta.