Deliver is a program for reliable and flexible local mail delivery. It's a perfect adjunct to your mail transport agent of choice (such as Sendmail or qmail). You can use it to kill spam, drop messages from specific senders, add a [LISTNAME] prefix to the subjects of messages that are delivered through mailing lists, and lots more.
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.
HTMLDOC converts HTML files and Web pages into indexed HTML, PostScript, and PDF files suitable for online viewing and printing. It can be used as a standalone GUI application, in a batch document processing environment, as a Web-based report generation application, or in embedded environments to support printing of HTML content. It runs on all Unix platforms as well as Mac OS X and Windows 2000 and higher.
John the Ripper is a fast password cracker, currently available for many flavors of Unix, Windows, DOS, BeOS, and OpenVMS. Its primary purpose is to detect weak Unix passwords. It supports several crypt(3) password hash types commonly found on Unix systems, as well as Windows LM hashes. On top of this, lots of other hashes and ciphers are added in the community-enhanced version (-jumbo), and some are added in John the Ripper Pro.
mail2news-easy is a utility that converts mail to news and news to mail. This program is unique in that it needs less configuration and modifying files than other products; it needs only one file, containing the signature of the mailing-list sender and the news name to which it relates. It installs easily, suppressing 100 of 100 modifications in the first install, and 75 of 100 when upgrading.
Heirloom mailx (formerly known as "nail") is derived from Berkeley Mail and provides the functionality of the System V and POSIX mailx commands. Additional features include support for MIME, IMAP (including caching and disconnected use), POP3, SMTP, S/MIME, international character sets, maildir folders, message threading, powerful search methods, scoring, and a Bayesian junk mail filter. Mailx can be used as a mail batch language in nearly the same way as it is used interactively. It can thus act as a mailbox filter, can fetch mail from remote accounts, and can send files as attachments.
Distributed Checksum Clearinghouse (DCC) is a system of clients and servers that collect and count checksums related to mail messages. The counts can be used by SMTP servers and mail user agents to detect and reject bulk mail. DCC servers can exchange common checksums. The checksums include values that are "fuzzy", or constant across common variations in bulk messages.
mapSoN is an anti-spam system that uses an approach which is entirely different than other systems. Instead of trying to recognize spam by the IP address of the SMTP dialog's peer or by certain patters in the mail's body, it uses the sender's email address to decide whether the e-mail is delivered to your mailbox or not: Any email that comes from a "known" address may pass, but any email that comes from an email address seen for the first time needs special confirmation before it may pass. "Special confirmation" means that mapSoN will generate an MD5 checksum of the to-be-confirmed email and store the email in a temporary spool directory. Then it sends a request for confirmation to the address from which the mail was coming. In this request, it will include the MD5 checksum and ask the recipient to reply back and to quote that MD5 hash. Once it sees that MD5 hash again, it considers that a confirmation of the original email, delivers the deferred email from the spool to your mailbox, and adds the sender's address to the database of known addresses, so that the next time he tries to contact you, his mail will pass through immediately. This heuristic catches almost any spam email, because spammers have to fake their sender addresses in order to avoid being held responsible for their abuse. Hence, their address will most likely not be in the database of known addresses, nor will they ever receive the request for confirmation email.