DSPAM is a scalable and open-source content-based spam filter designed for multi-user enterprise systems. On a properly configured system, many users experience results between 99.5% - 99.95%, or one error for every 200 to 2000 messages. DSPAM supports many different MTAs and can also be deployed as a stand-alone SMTP appliance. For developers, the DSPAM core engine (libdspam) can be easily incorporated directly into applications for drop-in filtering (GPL applies; commercial licenses are also available).

Features :-

1. System-wide administratively-maintenance free filtering. The DSPAM agent can integrate into just about any network and can even be implemented as an SMTP gateway.
2. A simple-to-use learning mechanism. DSPAM allows users to simply forward their spam to their "spam email address" for learning, eliminating any learning curve necessary to make it usable by your customers. The information used in every calculation is temporarily stored on the server, enabling DSPAM to relearn the original message by looking for a small signature in the forwarded spam. As a result, users don't have to be trained to 'bounce' messages around, and administrators don't have to worry about incompatible mail clients.
3. Support for a variety of storage implementations. DSPAM's storage driver API allows the administrator to choose how they wish to store data. Currently supported drivers include SQLite, Berkeley DB, MySQL, PostgreSQL, Oracle, and a self-contained high-speed hash driver.
4. Written in C for speed, performance, and scalability. Unlike Python or PERL solutions, DSPAM is written in a low-level compiled language, meaning there is very little overhead. DSPAM runs fast, efficient, and doesn't depend on any third-party language interpreters.
5. MTA support. DSPAM works great with Sendmail, Postfix, Qmail, Courier, and Exim, and should work well with many other MTAs. In the event you happen to run something like Exchange, DSPAM can be implemented on your network as an SMTP gateway. Just point your MX at it and configure it to relay to your mail server.

SPAM is eliminated before it gets to your Inbox or your computer. Messages that DSPAM thinks are spam are given a score. The higher the percentage, the higher the probability that the message is spam. Typically, this speeds up your perusal of those messages. Most people ignore anything that gets a score of 80% or higher.You have a graphical interface for training false-positives. That is, if DSPAM thinks that a message is spam, and it is not, you just click on the checkbox next to the message and tell it to your Inbox. Once that is done, DSPAM will remember that type of message and not keep thinking it is spam.