Postal is a fully featured, self-hosted mail server designed for websites and web applications that need reliable incoming and outgoing email delivery. Built in Ruby, it provides a complete alternative to commercial email services such as Sendgrid, Mailgun, and Postmark—without vendor lock-in or usage-based pricing. Postal handles SMTP inbound/outbound routing, email tracking, bounce handling, DKIM/SPF/DNS verification, and provides a web dashboard for monitoring delivery status. It’s ideal for developers, DevOps teams, and organizations that require full control over their email infrastructure, whether deploying on-premises or in the cloud.
With built-in APIs and a modern web interface, Postal enables teams to manage domains, track email delivery metrics, and automate email workflows without relying on third-party providers. Its modular architecture supports multi-tenant configurations and scalable deployments, making it suitable for startups to enterprises needing compliance, transparency, or cost efficiency in their email operations.
What You Get
- Full SMTP server with inbound/outbound support - Handles both sending and receiving emails via standard SMTP protocols, with TLS encryption and spam filtering integration.
- Web-based administration dashboard - Manage domains, users, queues, and delivery statistics through a real-time web interface accessible via browser.
- RESTful API for email sending and analytics - Programmatically send emails and retrieve delivery reports using a documented HTTP API with authentication tokens.
- DKIM, SPF, and DMARC support - Automatically generate and configure DNS records to improve email deliverability and prevent spoofing.
- Real-time delivery monitoring - View queue status, failed deliveries, bounce rates, and open/click tracking for sent emails directly in the UI.
- Multi-domain and multi-tenant support - Configure multiple domains with separate settings, users, and API keys for isolated email operations.
Common Use Cases
- Building a SaaS application with transactional emails - A startup uses Postal to send password resets, notifications, and invoices without paying per-email fees from Sendgrid or Mailgun.
- Enterprise email compliance and auditability - A financial institution deploys Postal on its private network to ensure all outbound emails are logged, monitored, and retained under data governance policies.
- Problem: High cost of commercial email APIs → Solution: Self-hosted Postal - A company spending $5k/month on Mailgun migrates to Postal running on a $10/month VPS, reducing costs by 98% while retaining feature parity.
- DevOps teams managing microservice email pipelines - A team using Kubernetes deploys Postal as a Helm chart to centralize email routing across 20+ microservices with centralized logging and rate limiting.
Under The Hood
The Postal project is a self-hosted email delivery platform built on Ruby on Rails, designed for high-volume transactional email handling with a focus on modular architecture and infrastructure-level control. It enables fine-grained management of email routing, IP pools, and organization-scoped configurations.
Architecture
This project adopts a monolithic Rails architecture with clear MVC separation and modular components tailored for email processing.
- Follows a configuration-driven design approach that supports scalable email infrastructure
- Organizes modules with well-defined boundaries and separation of concerns in controllers and models
- Employs Rails concerns and shared behaviors to reduce duplication across organizations
Tech Stack
Built using Ruby on Rails 7.0, the project leverages a modern web stack optimized for email delivery and deployment flexibility.
- Relies on Rails 7.0 with active record, action mailer, and custom configurations for database and OIDC integration
- Integrates Docker for containerization, Bundler for dependency management, and Rake for automation
- Supports comprehensive test environments with isolated runs and delivery method simulation
Code Quality
The codebase reflects a moderate quality level with consistent Rails conventions and a solid test suite covering key functionalities.
- Features a robust test suite that ensures API endpoint reliability and authentication flow integrity
- Implements custom exception handling alongside standard Ruby error patterns for better diagnostics
- Adheres to Rails conventions and uses modules for shared logic, promoting code consistency
- Shows signs of technical debt in controller before_actions and helper methods that could be refactored
What Makes It Unique
Postal stands out through its modular server architecture and infrastructure-level controls for email delivery optimization.
- Offers modular server-based configuration allowing granular control over email delivery settings per server
- Includes built-in IP pool management and endpoint routing for advanced traffic control and deliverability
- Uses Rails concerns and shared controller patterns to maintain DRY code while supporting multi-organization setups
- Provides consistent JSON/HTML response handling and comprehensive error management for integration ease