Trying to keep some kind of control over the ever-increasing flood of spam email that assaults email servers is a constant battle for email professionals. Whether the spam consists of advertisements for unneeded products and services, come-ons by fake mortgage lenders, shady offers for prescription pharmaceuticals, or outright pornography, the goal of email administrators is to keep all of this junk out of their users' Inbox. The main problem is the classic one of the Dutch boy and the dike: All...