Mailthe

Mailthe is an open-source software project and service for managing email delivery, testing, and analytics. It provides an API and an SMTP relay to help developers send transactional and marketing emails with visibility into delivery status and engagement metrics.

Mailthe originated in 2016 as a side project by developers seeking an easy-to-set-up mail relay with observable delivery events. It gathered a community in 2017 and released its first major version in 2018. The project is hosted on GitHub and follows an open-contribution model.

Key features include a RESTful API for sending messages, an SMTP-compatible relay, templating support, and event webhooks for delivery, opens, and clicks. It provides queueing and retry policies, built-in analytics, and role-based access control. It supports multiple delivery routes, including local SMTP, third-party ESPs, and MTAs.

Architecture and operation rely on a modular stack: a core relay, an API gateway, worker processes, and a data store. Typical deployments run on Docker or Kubernetes, with Redis or RabbitMQ for queues and PostgreSQL for metadata.

It is used by small to midsize applications for transactional emails, development testing, and marketing campaigns. The project emphasizes straightforward setup, good documentation, and a sandbox environment for testing without affecting production systems.

Reception has been positive for rapid initial setup and delivery visibility, though some enterprise users note limitations in high-scale throughput and advanced compliance features compared with commercial alternatives. See also: email delivery, SMTP, transactional email, API-based email services.