Exim is a message transfer agent developed at the University of Cambridge for use on Unix systems connected to the Internet. Freely available under the terms of the GNU General Public License, Exim can be configured to allow users to set up filter files as an alternative to the traditional '.forward' files. A filter file can test various characteristics of a message, including the contents of the headers and the start of the body, and direct delivery to specified addresses, files, or pipes according to what it finds. This makes it easy for us to help you filter out SPAM and viruses.