grepcidr can be used to filter a list of IP addresses against one or more Classless Inter-Domain Routing (CIDR) specifications, or arbitrary networks specified by an address range. As with grep, there are options to invert matching and load patterns from a file. grepcidr is capable of comparing thousands or even millions of IPs to networks with little memory usage and in reasonable computation time. It has endless uses in network software, including mail filtering and processing, network security, log analysis, and many custom applications.
fdm (fetch and deliver mail) is a simple, lightweight replacement for mail fetching, filtering, and delivery programs such as fetchmail and procmail. It can fetch using POP3, POP3S, IMAP, IMAPS, or stdin, and deliver to a pipe, file, maildir, mbox, or SMTP server, based on a set of regexps. It can be used for both single user and multiuser setups, and is designed with privilege separation when running as root.
Email Security through Procmail (the Procmail Sanitizer) provides methods to sanitize email, removing obvious exploit attempts and disabling the channels through which exploits are delivered. Facilities for detecting and blocking Trojan Horse exploits and worms are also provided.
cw is a non-intrusive real-time ANSI color wrapper for common Unix-based commands. It is designed to simulate the environment of the commands being executed, so that if a person types 'du', 'df', 'ping', etc. in their shell it will automatically color the output in real-time according to a definition file containing the color format desired. It has support for wildcard match coloring, tokenized coloring, headers/footers, case scenario coloring, command-line- dependent definition coloring, and includes over 50 pre- made definition files.
qSheff is a wrapper for the qmail queue that scans email for viruses and spam. After checking the message, it will wake the qmail queue. It is a replacement program for qscanq and RAV antivirus. It is simple and more powerful. It features the ability to quarantine, very nice logging, subject filtering, a blackhole, easy installation, and white/black lists.
XFMail is an X11 application for receiving electronic mail. It implements most of its email functionality internally so that it does not depend on a lot of extra packages. It supports POP3, MBOX, IMAP4, sendmail, and SMTP. It has built-in support for interfacing with PGP, GPG, ispell/aspell, faces, LDAP, and esound. It runs on most Unix variants.
mxallowd is a daemon for Linux Netfilter (using libnetfilter-queue) and BSD pf (using pflog) which implements a slightly improved nolisting mechanism. It requires your name server to be configured to return two MX IP addresses, and the one with higher priority must not run a mail server on port 25. mxallowd blocks attempts to connect to the mail server unless the sender tries to connect to the first mail server before the second. Since most spammers will attempt direct connections to each mail server, they will be blocked.