Postal

Postal is an open-source mail delivery platform designed for sending transactional email from applications using your own infrastructure. It provides SMTP and an HTTP API, plus a web interface to manage organizations, servers, credentials, and to inspect message activity.

Key Features

• SMTP server for application email delivery with per-server credentials
• HTTP API for sending messages programmatically
• Web-based administrative UI for managing organizations/servers/users
• Message tracking/logs for sent mail, including delivery attempts and status
• Support for multiple “mail servers” and separation by organization/team
• Domain and routing configuration tooling oriented around transactional mail

Use Cases

• Replace third-party transactional email providers for product emails (signups, password resets, receipts)
• Centralize outbound mail delivery for multiple apps/services with separate credentials
• Operate an internal email relay with auditing/visibility into outbound messages

Limitations and Considerations

• Primarily focused on outbound/transactional delivery (not a groupware mailbox server)
• Requires correct DNS and deliverability configuration (SPF/DKIM/DMARC) and ongoing reputation management

Postal is suitable when you need control over outbound email delivery, want an API/SMTP interface for applications, and need a UI for operational visibility. It provides the core primitives for delivering and tracking mail without relying on hosted email-sending services.