clapf is a high performance email content filter application. It includes a statistical (inverse chi-square) antispam module, an interface to several anti-virus products, and a Web UI (including a spam quarantine) written in PHP. It supports virtual users, URL- and IP-address blacklists, whitelists, LDAP directories, policy groups, minefield, and many more features. clapf can be used as an after queue content filter with Postfix (including as an appliance) and Exim or via the maildrop local delivery agent (LDA). It's also ideal to act as a spamfilter appliance in front of an Exchange server.