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

NewsFetcher monitors RSS and Atom feeds, tracking which items have been delivered, and sends new feed items as individual HTML emails using configurable mail delivery methods.

mail notification-ish tools