Manitou-Mail

Manitou-Mail is an open source database-driven Mail User-Agent.
Its user interface differs from other mail programs in that it's connected directly to your own mail database, rather than to your ISP or company's servers through the IMAP/POP3 and SMTP protocols.

The benefits are:

• Seamless handling of large volumes of email. Years of archive containing gigabytes are not a problem and don't alter the speed of getting to current messages.
• No local storage. Everything is stored inside the database, including filters and configuration information. The user interface can run off an USB key or an external drive. No backup is required when a client computer is replaced or upgraded.
• Advanced search and retrieval capabilites. The user interface provides stored searches and lets advanced users plug their own SQL queries if needed. The SQL language used directly is far superior to IMAP search extensions when it comes to complex queries, both in speed and capabilities. There's also a built-in full-text search engine for messages bodies and attachments.
• Robustness. Mailbox corruption and lost messages plague traditional mail programs. In Manitou-Mail, the data is kept safe from client-side crashes or bugs since all writing of the data is delegated to the PostgreSQL database server known for its robustness.
• Sharing. Multiple users can work concurrently on the same database. New messages are imported automatically into the database without the need for the user interface to run.
• Data openness. Querying the mail and associated data outside of the application is supported. The database schema is simple and documented, and the data is available in decoded form, including attachments. Hooking it up to other software such as a CRM system is straightforward.
• Customization. A unique feature of Manitou-Mail is that custom-made Perl functions can be plugged into the server-side mail workflow. Sample plugins are provided.

Unfortunately it's not straightforward. The server side of Manitou-Mail depends on these external components:

• A PostgreSQL server.
• A Mail Transfer Agent such as postfix, sendmail, exim, qmail... to which outgoing mail can be passed through a shell command.
• Optionally, a Mail Delivery Agent such as procmail or fetchmail. The manitou-mdx archive comes with a trivial MDA script that delivers mail in one file per message in a spool directory. The user has to make this script being called at the end of the delivery chain.

From the Manitou-Mail distribution available at the download page, these components need to be installed:

• the mail-database exchanger or manitou-mdx, a Perl program that runs server-side, available in source form or as a Debian package.
• The user interface, a desktop program for Unix or MS-Windows based on the cross-platform Qt library. It's available in source form, debian package for linux/x86, and .exe installer for Windows.
• The database creation and upgrade scripts, to be played manually.

  Free support

In addition to the mailing-list and forum available at the sourceforge project's page, the author is offering free support through email