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.
MIMEDefang is a flexible MIME email scanner designed to do all kinds of email processing, including anti-virus scanning, anti-spam scanning, replacing parts of messages with URLs, adding boilerplate disclaimers, and so on. It can alter or delete various parts of a MIME message according to a Perl-based policy filter. It can also bounce messages with unacceptable attachments and modify SMTP response codes on the fly. It works with the Sendmail 8.11 and newer "Milter" API, which makes it more flexible and efficient than procmail-based approaches.
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.
getmail is intended as a simple, secure, and reliable replacement for fetchmail. It retrieves email (either all messages, or only unread messages) from one or more POP3, SPDS, or IMAP4 servers (with or without SSL) for one or more email accounts, and reliably delivers into qmail-style Maildirs, mboxrd files, or through external MDAs (command deliveries) specified on a per-account basis. getmail also has excellent support for domain (multidrop) mailboxes, including delivering messages to different users or destinations based on the envelope recipient address.
Qmail-Scanner, (also known as scan4virus) is an addon that enables a Qmail Email server to scan all gatewayed Email for certain characteristics. It is typically used for its anti-virus protection functions, in which case it is used in conjunction with commercial virus scanners. but also enables a site to react to Email (at a server/site level) that contains specific strings in particular headers, or particular attachment filenames or types (e.g. *.VBS attachments). It also can be used as an archiving tool for auditing or backup purposes. Qmail-Scanner is integrated into the mail server at a lower level than some other Unix-based virus scanners, resulting in better performance. It is capable of scanning not only locally sent/received Email, but also Email that crosses the server in a relay capacity. It also has SpamAssassin support.
GNU m4 is an implementation of the traditional Unix macro processor. It is mostly SVR4 compatible, although it has some extensions (for example, handling more than 9 positional parameters to macros). GNU m4 also has built-in functions for including files, running shell commands, doing arithmetic, etc. Autoconf needs GNU m4 for generating `configure' scripts, but not for running them.
cats2procmailrc is a filter to generate a .procmailrc file from a much terser and friendlier file consisting mostly of single-line rules. These suffice to do the most common mail filing, making maintenance of a procmailrc very easy for someone with more than a few filing rules. Each rule normally names the folder, an optional subject tag, and the pattern. Raw procmail rules may also be included for those rare complex filings.