Haraka

Haraka is an SMTP server built on Node.js that handles thousands of concurrent connections and can deliver thousands of messages per second. It operates as a message transfer agent without providing mail storage, LDA, or IMAP services, and is typically paired with external mail stores or IMAP servers. The server includes a built‑in outbound delivery engine that automatically queues mail for relaying when authentication plugins are used.

The core of Haraka is a modular plugin architecture written in asynchronous JavaScript, allowing developers to add or replace functionality with a few lines of code. Plugins cover spam protection, HELO validation, DNS blocklist checks, DKIM signing, and integration with SpamAssassin, among many others. Configuration is managed through simple text files that list enabled plugins and define domain handling and forwarding rules.

Haraka is distributed under the MIT license, requires only Node.js to run, and can be installed globally via npm or from source. It is self‑hostable, free to use without subscription, and has a stable maturity level, making it suitable for high‑traffic sites that need a fast, extensible SMTP service.