The SpamAssassin spam detector expands the headers with a corresponding note, and the MTA then implements the processing of this information. SpamAssassin filters email in two phases: Phase 1 detects spam and phase 2 processes the email classified as spam. The client then retrieves the filtered mail but can also access the rejected mail if required. Depending on the result of the test, the email is either sorted into the user's mailboxes or moved to a special Spam folder. The Mail Transfer Agent (MTA) receives the incoming email and passes it to the spam filter, which returns it back to the MTA.

The best option to protect as many users as possible from unwanted email is to implement server-side spam filtering. In principle, email filtering can take place on the client or the server sides, and often the two approaches are combined. In practice, however, filters suffer from significant error rates, particularly false negatives, relegating legitimate email into the Junk mailbox. Sophisticated solutions like SpamAssassin use Bayesian filters, which are self-learning text filters that cull junk email on the basis of content – in theory, at least. You can come to grips with unwanted advertising email using a complex set of rules. Statistical tests and URL block lists are also used for spam detection and subsequent processing.įigure 1: SpamAssassin uses a variety of databases for analyzing and assessing email. A content filter checks the header and body content. Black and white lists explicitly exclude or include email addresses. Intelligent spam filters like SpamAssassin employ various solutions ( Figure 1).

Ideally, the filter should be located in the enterprise at the central node through which incoming email traffic runs and where the most efficient filtering is possible. Much like antivirus programs, spam protection needs to be updated continually if it is to provide protection. You can get the flood of advertising email under control to a certain degree with the use of spam filters. Spam is a dynamic, not a static, problem, and spammers usually respond very quickly and cleverly to countermeasures of any kind. The proportion of email advertising messages can be greater than 50 percent, forcing employees to check every piece of email and manually dump at least every second message in the Trash. Spam in your Inbox at home is a nuisance you can hardly avoid, but what is merely irritating at home is a genuine problem in the business world.

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