Email Filter

A technique used to organize incoming (and in some cases outbound) emails and to block email based on the IP address, specific and identifiable senders, keywords in the subject line, or by the quality of the content of an email. Most often this term refers to incoming email in order to filter out spam or messages that contain malicious code.

In regard to outgoing mail, a company may run all messages coming from internal sources to ensure that employees are adhering to any applicable laws directly affecting the particular business the organization is conducting.

Email filters can be installed as part of a stand-alone corporate requirement on all servers or as it applies to individual users. Filtering can be conducted solely by the ISP, which provides a minimum of protection. For many large organizations that have the resources and who also want to protect proprietary information from worms and viruses, it may be necessary to integrate many layers of protection.

Mail filters come in many configurations and the level of customization is directly controlled, in most cases, by a highly trained and experienced systems administrator. The software and code included will have varying degrees of configuration. Most are based on employing algorithms that will identify and match varying default or regular expressions. Other times, keywords in the message body are used, or perhaps the email address of the sender of the message. More advanced filters, like anti-spam filters, use a statistical document classification technique such as the naive Bayes classifier. Image filtering can also include those that use complex image analysis algorithms to detect skin-tones and specific body shapes normally associated with adult/pornographic images.