B's Harmaa is Postfix policy server that implements greylisting and sender policy framework. What differentiates it from other similar programs is its unique autowhitelist feature. When a request for delivery of a message is received by Postfix via SMTP, the triplet CLIENT_IP / SENDER / RECIPIENT is built. If it is the first time that this triplet is seen or if the triplet was first seen less than one minute ago, then the message gets rejected with a temporary error. Spammers often will not try again later, even though it is required per RFC.
Pymadea (PYthon MAil DElivery Agent) is a simple replacement for procmail. Configuration files are ordinary Python scripts. Modules from the standard library are used where possible. It consists of a set of useful scripts that are helpful for using Python as an MDA, rather than a normal, standalone application.
libmime is a MIME parser in the same vein as Expat, the stream-oriented XML parser. As input is fed to the parser, events are generated which an application can catch by registering event handlers. Such events include the Unix From_ line, start of entity, end of entity, entity boundary, header, end of headers, and body. libmime supports MIME message editing through a delta mechanism. Edit contexts are instantiated and changes applied to specific contexts. Edit contexts can then be expressed in standard unified diff format which, when applied to the input source stream, will result in the new message.
SeeYouLater's purpose is to fetch a list of IPs of known spammers and to ban them by putting them in /etc/hosts.deny. /etc/hosts.deny is usually read by xinetd or daemons using tcpwrapper. The software is composed of: the feeder, that looks at SMTP daemon logs for the string ++BAN:IP++ and feeds the database accordindly; and the butcher, that looks at the database and updates /etc/hosts.deny. You may want to run the butcher on a system that has no access to the SMTP logfiles, but you can install both packages on the same system. It has been written to run with Exim.