Posthorn

Posthorn is a self-hosted email gateway that sits between your applications and transactional mail providers like Postmark, Resend, Mailgun, or AWS SES. It eliminates the need to run a mail server and centralizes email configuration across your stack. The project was built using Claude Code.

It supports three ingress methods: HTTP forms (for contact forms and webhooks), JSON API (for workers and cron jobs), and SMTP (for apps like Ghost, Gitea, and Mastodon). Posthorn handles security features including honeypot fields, rate limiting, and CSRF protection, while managing retries, bounce handling, and sender authentication through a single configuration file.