Manitou-Mail

Manitou is a database-driven mail user-agent and associated utilities. It provides a framework and tools for storing and exposing mail as organized data, accessible by SQL. It is aimed at seamlessly handling large mailboxes, possibly processed by multiple concurrent users. In addition to the features commonly found in traditional mail programs, its user interface (C++/Qt) aims at providing some more unique, database oriented ways to organize, process and retrieve mail messages.

Manitou is also free software, released under the GNU Public License. Read the full license text.

Components

Here is how it fits into the chain of mail programs:

Manitou-Mail consists of:

A PostgreSQL script that creates the database objects (tables, functions, triggers and sequences) that will contain the mail data.
A perl script that imports incoming mail or mailboxes into the database, and delivers outgoing messages to the mail transport system. It is named manitou-mdx, the mdx suffix standing for "mail/database exchanger". This program is intended to mostly run as a daemon, waiting for incoming mail to incorporate or outgoing mail to pass to sendmail. It is responsible for the MIME encoding and decoding, for applying filters and generally carrying on the automated actions needed to process the mail.
A graphical user interface based on the Qt library and running under Unix/X-Window, Microsoft Windows, or MacOS X. The user interface is only connected to the PostgreSQL database (it doesn't do any smtp, pop3, imap or similar, but only SQL). In addition to extended search capabilities, the interface provides the same kind of features as traditional mail user agents.
The database, mdx and user interface can run on the same machine or on different nodes of a network.