Haraka is a free open source Node.js SMTP server with a plugin architecture. Read our 2026 review of features, use cases, pros, cons and alternatives.
Category
Communication
Pricing
Open Source / Free, from Free
Verified
Not yet
Last updated
July 18, 2026
Founded
2011
Free PlanAPIOpen SourceSelf-Hosted
Overview
Haraka is a free, open source SMTP mail server written in Node.js, built for high-throughput, asynchronous mail handling with a fully extensible JavaScript plugin architecture, released under the MIT license.
Created by Matt Sergeant in 2011 and inspired by the Qpsmtpd mail server, Haraka is community-maintained on GitHub with no corporate owner, currently led by maintainer Matt Simerson.
Key Features
Haraka's event-driven, non-blocking architecture lets a single server process handle thousands of simultaneous SMTP connections, with behavior customized entirely through JavaScript plugins hooked into each stage of the SMTP transaction.
A large plugin registry covers authentication, DKIM signing, DNS blocklist checking, SpamAssassin and rspamd integration, and ClamAV antivirus scanning, and Haraka can run as either an inbound filtering gateway or an outbound submission agent.
Pricing
Haraka is completely free and open source under the MIT license, with no paid tiers, commercial edition or vendor lock-in.
Anyone can download, modify, self-host and redistribute Haraka without cost, and there is no company selling a hosted or supported commercial version.
Key Features
Event-driven architecture — Node.js's non-blocking I/O model lets a single process handle thousands of simultaneous SMTP connections.
JavaScript plugin system — Plugins hook into every stage of the SMTP transaction to inspect, modify, accept or reject messages.
DKIM signing and verification — Built-in support for signing and verifying DKIM to authenticate outbound and inbound mail.
DNS blocklist checking — Plugins check DNSBLs to filter known spam and abuse sources before accepting mail.
Spam and antivirus integration — Integrates with SpamAssassin, rspamd and ClamAV for spam scoring and malware scanning.
Flexible deployment modes — Runs as an inbound filtering gateway in front of Postfix or as a full outbound mail submission agent.
High connection throughput — Handles thousands of concurrent connections and messages per second in production.
MIT licensed and free — Fully open source with no cost, commercial edition or licensing restrictions.
Pros & Cons
Pros
Free and open source under the permissive MIT license
Handles very high SMTP connection volume and throughput
Highly extensible through a JavaScript plugin architecture
Long track record in production since 2011
Battle-tested at scale by companies like Craigslist
Cons
Requires Node.js and JavaScript expertise to configure and extend
No official graphical management dashboard
Documentation is community-maintained and can be sparse in places
Not a hosted or managed SaaS, so self-hosting carries operational burden
Smaller community and install base than Postfix or Exim
Pricing
Haraka Free Free, open source, no billing
Frequently Asked Questions
What is Haraka?
Haraka is a free, open source SMTP mail server written in Node.js, designed for high-throughput, asynchronous mail handling with a fully extensible JavaScript plugin architecture.
Is Haraka free?
Yes, Haraka is completely free and open source under the MIT license, with no paid tiers or commercial edition.
Who maintains Haraka?
Haraka was created by Matt Sergeant and is now community-maintained on GitHub, currently led by maintainer Matt Simerson.
What is Haraka used for?
Haraka is used to operate high-throughput inbound mail filtering gateways or outbound mail submission agents, and is used in production by companies like Craigslist.
Does Haraka support spam filtering?
Yes, Haraka integrates with SpamAssassin and rspamd for spam scoring and supports DNS blocklist checking through plugins.
Can I write custom plugins for Haraka?
Yes, Haraka's behavior is customized entirely through JavaScript plugins that hook into each stage of the SMTP transaction.