Mailchimp Transactional API
Mailchimp Transactional is a powerful email delivery service that lets you send personalized, one-to-one emails like password resets, order confirmations, and welcome messages.
Resources
Documentation
https://mailchimp.com/developer/transactional/docs/fundamentals/
Guide
https://mailchimp.com/developer/transactional/guides/quick-start/
Authentication
https://mailchimp.com/developer/transactional/docs/authentication-delivery/
Webhooks
https://mailchimp.com/developer/transactional/docs/webhooks/