How Do Spam Filters Work

Email spam filters are software programs designed to filter and get rid of spam. They provide a viable alternative to manually deleting large numbers of junk email every day. They are a useful tool for people who use emails on a daily basis, as they can quickly sort through irrelevant messages. For their maximum utilization, it is important to have a basic understanding of how spam filters work. Mishandling of a spam filter can result in the inbox getting flooded with junk or the user constantly searching for misplaced messages. By using an email spam filter, the users can see all the emails that were filtered and mark them as 'not spam', if they do not consider them as such and want to retain them. Most email sites are configured to have inbuilt spam filters.

Types of Email Spam Filters
Depending on their functionality and uses, there are different types of filters. Some of them are as follows.

• User defined filters
• Header filters
• Language filters
• Content filters
• Permission filters

Working of Spam Filters
Spam filters follow a point system which enables them to filter out the unnecessary emails. They generally tag the mails as spam, depending on certain words or phrases that are most commonly found in spam emails. Generally, spammers try to make their mails appear lucrative, by tagging them as 'exciting news' or with different types of attractive word combinations. However, this makes the spam mails predictable and recognizable, and because of that, spam filters can look for certain regular key words and phrases which are repeated often. Some of the most common words used in spam are 'millionaire', 'Viagra' and 'sex'. Phrases that urge the users with tempting prizes are also flagged. Things like excessive exclamation marks, loud words (all caps), etc, can mean that the email is deemed to be spam. Besides the key-word search, spam filters follow three more tests to ensure the authenticity and reliability or otherwise of emails.

• Format of the Mail: The spam filters check out the format and design of the mail to ensure that there are no excessive external links or hidden text. This enables them to make a choice between a normal mail and a spam.
• Black Lists: The filters utilize black lists which are a collection of IP addresses and domain names that have sent out spam in the past. Spam filters check the sender of the email and look out to see if his domain or mail server's IP address is on a black list. If found, the email is refused or put into the spam list.
• Scanning the Attachments: It is important for the filters to check the files which are attached to the email. This enables them to catch viruses and Spyware, before they get to the receiver's computer.

The points allotted to all these tests add up to a certain number, which in turn is considered for tagging the email as spam or not. Suppose the spam filter comes across an email sent by an IP address which is not in the black list, points are calculated based on each of the other tests. If the attachment with the email is not too big or too small, it is given 1 point and in case the formatting looks bad, another 2 points are given. As the sender's IP address is not present in the black list, zero points are given for this test. The total comes out to be 3 points. Now, if the spam filter is configured to block things that add up to 6 points or more, the mail goes into the inbox of the user. But in case it is allowed to block things which get 3 points or above, the mail gets blocked.

Spam filters block all emails that do not come from an approved source or show properties of regular spam. However, no scan or filter is ever perfect, as spammers keep on coming up with new ideas, trying to find ways to target a customer's inbox.