Introduction

rblsd is a small, fast, SpamAssassin-compatible spam filter. The only test performed is a series of RBL (DNSBL) lookups on the path of each message. This results in fast, accurate, low-load spam filtration. rblsd can be used as a standalone, drop-in replacement for SpamAssassin, or in conjunction with SpamAssassin to increase mail throughput.

Benefits of using RBL's:

  • RBL's are updated in real time, and their accuracy does not depend on the age of the software that you install.
  • Tests operate at the speed of DNS queries and require negligible processing power.
  • Tests can be performed asynchronously without a loss in performance.
  • RBL accuracy depends on the source of the message and cannot easily be forged by the spammer.
  • Spammers cannot put anything in the body of the message (such as random words or phrases designed to throw off learning-based filters) that will fool RBL-based filters.
  • The organizations that provide RBL's dedicate their time to discovering spammers. A spammer can be immediately neutralized once discovered if the server-side uses an RBL filter.

Benefits of using rblsd over other RBL-filters:

  • rblsd performs queries asynchronously and can handle several clients at once.
  • rblsd is equipped with configurable rules designed to maximize spam filtration while minimizing false positives.
  • rblsd performs RBL lookups on IP addresses found in the Received headers of the message, rather than just the incoming connection.
  • If you have installed SpamAssassin, you will be able to very easily install rblsd.
  • rblsd can be used as a primary filter to SpamAssassin, such that messages not tagged by rblsd will continue to SpamAssassin. Reducing the number of messages that get passed to SpamAssassin will reduce the amount of CPU time spent processing messages, resulting in faster message throughput.
  • rblsd was written entirely in C with a top priority of efficiency. There is no interpreter overhead and the process consumes less memory (on average) than a shell.

For more detailed information on how rblsd works and the setup required, see the README file.