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.
GNU parallel is a shell tool for executing jobs in parallel locally or using remote computers. A job is typically a single command or a small script that has to be run for each of the lines in the input. The typical input is a list of files, a list of hosts, a list of users, a list of URLs, or a list of tables. If you use xargs today you will find GNU parallel very easy to use, as GNU parallel is written to have the same options as xargs. If you write loops in shell, you will find GNU parallel may be able to replace most of the loops and make them run faster by running several jobs in parallel. If you use ppss or pexec you will find GNU parallel will often make the command easier to read. GNU parallel makes sure output from the commands is the same output as you would get had you run the commands sequentially. This makes it possible to use output from GNU parallel as input for other programs.
yaspi (Yosi's Anti-Spam POP3 fIlter bot) is a POP3 mail-scanner specifically made to combat mail bombings caused by viruses (i.e. Swen). It connects to the POP3 server, inspects the messages, and deletes the infected ones without ever downloading them. Its most interesting feature is that it can automatically send abuse reports to the ISPs from which the infected mails originated.
Dkfilter is a DomainKeys implementation for the Postfix mail transfer agent. It is implemented as two filters (or SMTP proxies). There is an "outbound" filter for adding DomainKeys signatures to outgoing email and an "inbound" filter for verifying signatures of incoming email. The filters can be plugged into Postfix as either Before-Queue or After-Queue Postfix content filters. For more information about DomainKeys, see http://antispam.yahoo.com/domainkeys.
dkimproxy is an SMTP proxy that signs and/or verifies Domain Keys Identified Mail (DKIM). It is designed to work with Postfix. It comprises two separate proxies: an "outbound" proxy for signing outgoing email, and an "inbound" proxy for verifying signatures of incoming email. With Postfix, the proxies can operate as either Before-Queue or After-Queue content filters.
DSPAM is a server-side statistical anti-spam agent for Unix email servers. It masquerades as the email server's local delivery agent and effectively filters spam using a combination of de-obfuscation techniques, specialized algorithms, and statistical analysis. The result is an administratively maintenance-free, self-learning anti-spam tool. DSPAM has yielded real-world success rates beyond 99.9% accuracy with less than a 0.01% chance of false positives.
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.
spamdyke is a drop-in filter for qmail to provide connection-time blacklisting, graylisting, DNS RBL/RHSBL checking, sender MX checking, improved logging, and more. spamdyke will provide SMTP AUTH and TLS to unpatched qmail servers. Installing spamdyke does not require patching or recompiling qmail.