Haraka

Haraka is an open source, event-driven SMTP server written in Node.js. It is designed for high throughput and concurrency, and is commonly deployed as a filtering MTA or mail submission agent (MSA) via a flexible plugin system.

Key Features

• Modular plugin architecture to customize SMTP behavior and mail processing
• High-performance asynchronous design suitable for thousands of concurrent connections
• Built-in outbound delivery and queueing for authenticated/relayed messages
• Supports common email authentication and policy needs via plugins (for example DKIM and SPF)
• Useful as a filtering layer alongside a separate mail store and IMAP server

Use Cases

• Run a high-throughput SMTP front-end with custom filtering and routing rules
• Deploy an MSA on port 587 with authentication and outbound signing policies
• Add specialized anti-spam and validation logic in front of an existing mail system

Haraka is a strong fit when you want a programmable SMTP server that is easy to extend in JavaScript and integrates with existing mail storage and IMAP solutions. Its plugin ecosystem enables practical customization without modifying the core server.