xtee (cross-tee/expanded tee) is a program for building complex pipelines. It resembles the tee command, except that instead of copying stdin to stdout, it copies an input file to stdout and stdin to an output file. You can use xtee for building things like a bidirectional HTTP filter (using netcat and sed).
dgrey is a greylisting policy server that allows greylist information to be synchronized between multiple mail servers. All information is shared between the nodes and the nodes are equal; there is no master. The nodes may lose communication for a while and still be able to correctly resynchronize later. This works because all nodes keep a log of changes to the database. All communication is done across TCP connections, which can optionally be password protected. dgrey works with mail transfer agents such as Postfix and Exim.
Artica for Postfix is a secure Web interface for Postfix administration. It is designed to reduce the cost of creating and managing a full Linux mail server. It supports Postfix, Kaspersky Anti-spam, Kaspersky Anti-Virus, Bogofilter, Milter-greylist, SpamAssassin, Clam Antivirus, Amavis, OpenLDAP, SQLite library, Cyrus-imap, Procmail, Fetchmail, DnsMasq, Mailman, Sieve, Yorel script, QueueGraph, MailGraph, AWSTats, geoip, and more.