Full list of features

ZoneMTA is a Modern, high performance, plugin driven outbound SMTP relay (MTA/MSA) built on top of Node.js and MongoDB (as queue storage). Designed from the ground up for High throughput and email deliverability as main goals. Haraka comes stripped out of any bells and whistles that could slow it down, then you can add as many bells as you require and whistles as required using plugins.

Full List of features:

• Web interface. See queue status and debug deferred messages through an easy to use web interface (needs to be installed separately).
• Cross platform. You can run ZoneMTA even on Windows
• Fast. Send millions of messages per day
• Send large messages with low overhead
• Automatic DKIM signing
• Adds Message-Id and Date headers if missing
• Sending Zone support: send different messages using different IP addresses
• Built-in support for delayed messages. Just use a future value in the Date header and the message is not sent out before that time
• Assign specific recipient domains to specific Sending Zones
• Queue is stored in MongoDB
• Built in IPv6 support
• Reports to Prometheus
• Uses STARTTLS for outgoing messages by default, so no broken padlock images in Gmail
• Smarter bounce handling
• Throttling per Sending Zone connection
• Spam detection using Rspamd
• HTTP API to send messages
• Custom plugins
• Automatic back-off if an IP address gets blacklisted
• Email Address Internationalization (EAI) and SMTPUTF8 extension. Send mail to unicode addresses like андрис@уайлддак.орг
• Delivery to HTTP using POST instead of SMTP

High Performance, send milions of emails per day on standard hardware.

Higly Scalable, You can proxy incoming requests to several nodes, those nodes can use one single Database if required

• Higly extendable. With its plugin architecture, you are in full control. i. Easily extendable using plugins, which are way more flexible than milters. Plugin architecture. Easily extendable using plugins, which are way more flexible than milters.

Ability to use multiple local IP addresses.

Granular control over routing of every single message. Trusted senders can be routed through high-speed (more parallel connections) virtual "sending zones" that use high reputation IP addresses, less trusted senders can be routed through slower (less connections) virtual "sending zones" or through IP addresses with less reputation. In addition the server comes packed with features more common to commercial software, ie. message rewriting, IP warm-up or HTTP API for posting messages.

There's also a web-based administration interface (needs to be installed separately).