Quick Spam Filter (QSF) is an Open Source email classification filter, designed to be small, fast, and accurate, which works to classify incoming email as either spam or non-spam.

QSF's targets are speed, accuracy and simplicity:
* It is small and is written in C so it starts up quickly, unlike filters
written in Perl.
* It understands MIME and HTML, so it can intelligently deal with modern
spam, unlike older Bayesian filters such as ifile.
* It runs as an inline filter rather than as a daemon, so it is simple to
install.
* It is written to do only one job - decide whether an email is spam or not
using the content of the message alone - so it is less complex than filters
such as SpamAssassin. Less complexity means bugs and security problems are
less likely.
* As well as words and word pairs, QSF also spots special patterns in email
such as runs of gibberish, HTML comments embedded in text, and other common
spam giveaways, and its flexible tokeniser allows more patterns to be added
as spammers change their tactics.