Cuttlefish

Cuttlefish is a self-hosted, open-source transactional email server built on Postfix that accepts outbound email from applications via standard SMTP and delivers it reliably. It provides a web UI with real-time analytics, automatic bounce handling, open and click tracking, DKIM signing, and a GraphQL API for programmatic access. Multiple applications can each have their own SMTP authentication credentials, and IP reputation can be checked with a single click. It is a free, vendor-lock-in-free alternative to commercial services like SendGrid and Mailgun.