spam filtering

To prevent email spam (a.k.a. unsolicited bulk email), both end users and administrators of email systems use various anti-spam techniques. Some of these techniques may be embedded in products, services and software to ease the burden on users and administrators. No technique is a complete solution to the spam problem, and each has trade-offs between incorrectly rejecting legitimate email (false positives) vs. not rejecting all spam (false negatives), and the associated costs in time and effort. Anti-spam techniques can be broken into four broad categories: those that require actions by individuals, those that can be automated by email administrators, those that can be automated by email senders and those employed by researchers and law enforcement officials.