Postal Mail Server

Postal is a complete and fully featured mail server for use by websites and web servers, designed to provide a scalable, self-hosted alternative to commercial email delivery services like SendGrid, Mailgun, and Postmark. Originally developed by Adam Cooke at aTech Media (UK) in 2009 as a commercial product and open-sourced in 2017, Postal has over 15,000 stars as of 2026. Written in Ruby on Rails with a Go-based SMTP server, Postal is designed for high-volume transactional email delivery and provides a comprehensive API for programmatic email sending. Key features include: multi-organization and multi-server architecture (managing multiple mail servers for different clients or projects from a single installation), API-first design with REST API and webhooks for real-time delivery notifications (sent, delivered, bounced, held, delayed), SMTP relay for integration with any application capable of sending email, message tagging and categorization for organizing and filtering email streams, per-organization and per-server credential management, IP pools for distributing outgoing email across multiple IP addresses, DKIM and SPF signing for email authentication, DMARC and ARC support, suppression list management (automatically suppressing bounced addresses), click and open tracking (via tracking pixels and link wrapping), inbound email processing (receiving emails via SMTP and forwarding to HTTP endpoints or other addresses), raw message access (storing and retrieving raw RFC 822 email content), queue management with retry logic and exponential backoff, dedicated IP addresses, throttling and rate limiting per server or domain, and a web admin interface with real-time delivery statistics and message logs.