Spam Filter

Spam means the bulk of unsolicited emails that you receive. It is very annoying as most of it is actually useless. A Spam filter is software that will help to capture and check the mails that resemble Spam before it is delivered to your email inbox. This filter might let the message pass unchanged, discard the message or redirect the message to some other recipient. There are some filters available that are capable of editing the content of the messages even before they are sent.

The most common use that this filter is put to is to remove both computer viruses and Spam. It is also used to check the outgoing mails. This policy is followed by some companies to make sure that the employees are complying with the company rules and regulations. A filter might also be used to rate messages according to their importance, sort them and put them into separate folders according to the subject matter or any other criteria.

Configurability is varied in the mail filters. It is done on the basis of matching a particular regular expression. Often the key words in the message are the criteria or the sender’s email address is also taken into consideration. There are some other types of the more advanced filters that are available and they use the statistical document classification methods for example the Bayes classifier.

Procmail is an agent that delivers mail or it is a mail filter. It is a program devised to process the incoming mails in the computer. It is usually used in the UNIX systems. It has been invoked from Sendmail. Thus the mail processing becomes event driven. Procmail has a companion tool that is known as the formail. Formail allows procmail to batch process the mail that is already there in your mail inbox. Procmail carries out the common operations like sorting and filtering of emails. It puts the different mails into the different folders made according to the keywords in the from or to title bars, text or the subject of the mail or even the sending of the auto replies. There are also other more sophisticated operations that are possible. A very common practice is letting the procmail to call an externalized Spam filter program known as the Spam Assassin. It is also known because of its source code that can hardly be read.

Sieve is another mail filtering language and it is used to create filters for all emails. This language does not need any mail architecture or operating system in particular. The messages need to be RFC 822 compliant. Sieve is in many ways different from the highly limited traditional programming languages. It has no loops, no variables in the base standard, prevents the runaway programs and also limits the language to the simple filtering operations.

Some other types of Spam filters are Netintelligence, Markovian discrimination and Bayesian Spam filtering. Each of these have their own special features and different companies use them to control the menace called Spam.