Clam AntiVirus is an anti-virus toolkit designed especially for email scanning on mail gateways. It provides a number of utilities, including a flexible and scalable multi-threaded daemon, a commandline scanner, and a tool for automatic database updates. The core of the package is an anti-virus engine available as a shared library.
mod_mocrify provides a handler to remove unnecessary whitespace from HTML pages before they are transmitted. It also is capable of making your HTML source virtually unreadable to human eyes by replacing all displayed characters with their ASCII code entity representation. All these modifications do not affect the layout in any way.
Amber sits in the tcpserver chain for qmail and implements an "amber list" for incoming mail. This neither accepts nor rejects connections, but implements a number of timing-related tricks to fake out spam and virus software that doesn't implement SMTP correctly. For example, it can defer requests from new IP addresses for a few minutes before it starts passing connections on to smtpd, pause and check for programs that send data before the HELO, and otherwise make things rough for bandit bulk mailers.
rbldnsd is a small and fast DNS daemon inspired by D. J. Bernstein's rbldns that was designed to serve DNSBL zones. It is extremely fast, outperforming both bind and djbdns greatly, has a very small memory footprint, and can serve both IP-based (ordb.org, dsbl.org, etc.) and name-based (rfc- ignorant.org) blocklists. Unlike rbldns, it has the ability to specify individual values for every entry, can serve many zones on a single IP address, and can reply to DNS metadata requests. The daemon keeps all zones in memory for faster operation, but its memory usage is very efficient, especially for repeated TXT values, which are stored only once.