postalserver/postal

Postal is a full-featured open-source mail delivery platform for sending and receiving email, designed to be self-hosted on your own servers. The README describes it as comparable to commercial email delivery services like Sendgrid, Mailgun, or Postmark, but free to run yourself. Those services handle the infrastructure for sending transactional emails (like password resets, order confirmations, and notifications) on behalf of websites and web applications. By running Postal yourself, you own the email infrastructure rather than paying a third-party service and being subject to their pricing and data policies. It handles both outgoing mail (SMTP, the standard protocol for sending email) and incoming mail. The project is written in Ruby and is available with installation documentation and a full feature list on its documentation site. The README itself is sparse and points to external documentation for setup details.