Mailman makes it easy to process incoming emails with a simple routing DSL

Qup is a generalized API for Message Queue and Publish/Subscribe messaging patterns with the ability to plug in an appropriate messaging infrastructure based upon your needs. Qup ships with support for (https://github.com/robey/kestrel), (http://redis.io), and a filesystem infrastructure based on...

Uses the maildir gem to store ActionMailer deliveries.

This provides the implementation of a user and email store for an EventMachine-based SMTP and POP3 server.

A simple queue API with a maildir backend. Also includes an HTTP API

mail notification-ish tools