Response is a set of tools to handle automatic email responses, also called "Out of Office", "Vacation", or "Autoreply" messages. Response tries hard to do that the correct way, i.e. not responding to messages that should not be responded to. All of the validation code can be easily modified to suite your needs, but the project tries hard to ship sane defaults. It is designed for many virtual users and multiple mail servers, but works just fine for small deployments. Configuration and response state is stored in an RDBMS.
BarricadeMX provides very accurate, high performance spam and virus protection for Enterprise and ISP sites. Features include simple installation and administration, little if any end user interaction required, no quarrantine required, and an optional custom non-delivery receipt for all rejected messages. It uses a custom version of SpamAssassin along with many proprietary anti-spam techniques to achieve a guaranteed level of over 99% accurate spam detection with fewer than 0.1% false positives.
OpenFWTK is an application proxy toolkit which inherits the ideology of TIS fwtk and maintains API backwards compatibility. The design goal is to make it simple yet powerful; no performance hacks are allowed in the code and library dependencies are reduced to a minimum. It is a true application layer filter. It features unified pluggable content inspection for the most frequently used protocols, NAC (Network Admission Control), and the ability to define fine-grained Internet access policy based on browser identification.
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.
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.
milter-spamassassin is a lightweight, reliable, and fast Sendmail plug-in for the SpamAssassin mail filter. It uses advanced statistical and heuristic tests to identify SPAM built into spamd (the SpamAssassin daemon program). This filter has a hosts/networks whitelist, scans messages less than a defined size, rejects SPAM messages at the DATA stage of SMTP session, copies SPAM messages into the special "garbage" mailbox, performs Subject tagging if SPAM is detected, and adds an information header to scanned messages.
milter-clamav is a lightweight, reliable, and fast Sendmail plug-in for the ClamAV antivirus scanner. It uses a mail scanning engine built into clamd (the ClamAV daemon program). This filter scans messages less than a defined size, rejects infected messages at the DATA stage of SMTP session, and adds an information header to scanned messages.