A set of instructions for configuring Exim to encrypt every piece of incoming mail by running it through GnuPG before it hits your mail queue. This is used for protecting your e-mail on disk when you don't fully trust your mail server (say, you have a VPS as your mail server, or you don't trust the physical security of where you have your server racked).
Note that you'll have to configure your mail client to transparently run GnuPG to decrypt everything.