IndiMail is a messaging platform built using qmail and other messaging software. IndiMail has the ability to distribute the users in a domain across multiple hosts. IndiMail has multiple queues (called a queue collection), which can achiever very high concurrencies. The system IDs and configuration files used by IndiMail are all configurable through a set of environment variables, allowing you to customize IndiMail the way you want. IndiMail does not use hard-coded uid/gid in the executables, which makes it easy to distribute a binary package. IndiMail has features that any modern email server should have: SMTP, QMQP, QMTP, IMAP, POP3, DKIM, BATV, greylisting, filtering capability, and spam/virus control.
Maildrop is a powerful email filter/delivery agent. It supports mbox-style mailboxes and maildirs (a mail storage format used by Qmail). Its mail filtering language supports RFC822 parsing and GDBM/Berkeley DB database files. The maildrop package also includes a command-line tool to perform various operations on MIME messages.
Kolab is a groupware system that provides a comprehensive and flexible solution for workgroups. Email, contacts, and group calendars can be managed via the Web, Windows/Outlook, and Linux/KDE. It supports offline synchronization and full seamless support of mixed client environments because the Kolab-XML storage format is fully open and avoids MAPI/TNEF.
lib_MTA is a BASH function library for dealing with email. It provides support for unencrypted and TLS-encrypted relaying of email with attachments, special mailing list filtering, and From address spoofing. The installation automatically sets up a mailing list filtering infrastructure that can be enabled with a few simple steps. Example scripts for relaying email and filtering mailing lists are included in the package with the library. Desktop users can employee a simple script to send email to remote addresses without the need for a local MTA, provided they have relay access via Gmail or their ISP.
Response is a set of tools to handle automatic email responses, also called "Out of Office", "Vacation", or "Autoreply" messages. Response tries hard to do that the correct way, i.e. not responding to messages that should not be responded to. All of the validation code can be easily modified to suite your needs, but the project tries hard to ship sane defaults. It is designed for many virtual users and multiple mail servers, but works just fine for small deployments. Configuration and response state is stored in an RDBMS.