Spampig DnsblCheck takes the IP address of a mail server and looks it up in common blacklists and whitelists. The program tests against the major block lists from Spamhaus, SORBS, Spamcop, Barracuda, UCEProtect, and others. In addition to blacklists, it also checks against IP address and domain name whitelists and even checks PTR record integrity. The program returns results quickly, typically in less than a few seconds. If you don't get results quickly, it indicates you may have DNS problems and knowing this can also be useful. This application can be useful to spam fighters and email users who are struggling to find out why their messages are being blocked.
pgl4rbl implements a Postfix policy server that mixes two widely used techniques: greylisting and RBL (DNS blacklists). The idea is that greylisting is applied only to SMTP clients that match a RBL; this means that normal clients are not delayed (such as with a normal greylisting implementation), and RBL false positives do not cause problems (like when outright blocking them at the SMTP level).
Rspamd is an anti-spam system designed to work faster than SpamAssassin by using the event model and various optimizations. Its most important features include regexp and Lua rules for filtering different parts of messages, a number of built-in functions for analyzing messages, fuzzy hash support, SURBL filters, email and character table support, a control interface for remote managing and stats gathering, a Lua plugin system, statistics support (OSB/Bayes), and an AJAX-based Web interface.