https://github.com/haraka/Haraka

Haraka is a highly scalable node.js email server with a modular plugin architecture. Haraka can serve thousands of concurrent connections and deliver thousands of messages per second. Haraka and plugins are written in asynchronous JS and are very fast.

Haraka has very good spam protection (see plugins) and works well as a filtering MTA. It also works well as a MSA running on port 587 with auth and dkim_sign plugins enabled.

Haraka makes no attempt to be a mail store (like Exchange or Postfix/Exim/Qmail), a LDA, nor an IMAP server (like Dovecot or Courier). Haraka is typically used with such systems.

Haraka has a scalable outbound mail delivery engine built in. Mail marked as relaying (such as via an auth plugin) is automatically queued for outbound delivery.

It looks strange. But I can imagine that it could be useful.