Understanding How Spam Filters Works

If you are active online, then you know how annoying it is to check your emails and get rid of a bunch of unsolicited commercial messages. While some are for marketing purposes, some are designed for phishing attacks, which could be very dangerous.

Billions of messages are being sent on a daily basis, and about half of those are 'spams'. So how do you manage your emails in such a way that you won't have to filter them out manually?

This is when a spam filter comes in handy.

What Is a Spam Filter?

As the term suggests, this program can be used to detect and prevent unwanted emails from getting into your inbox. Initially, this feature was designed simply to identify whether a certain message is spam or not. If it is, it will go directly to the spam folder. But this process has evolved over the years. Some mailbox providers have integrated better spam filters that can categorize the emails accordingly.

How Does It Work?

There are many types of spam filters, but their common goal is to decipher the header data, check if the sender is part of the blacklists, and filter the content so the email can be pointed to the right folder.

Header Information

You are probably not aware, but for every email, there is so-called header information. This data contains the IP address of the sender, date and time stamps, as well as other stuff that tells about the origin of the email. They can be tricky, but this is one of the advantages of spam filters. They catch any attempt to deceive the receiver as the addresses are cross-checked with the list of spammers.


Internet service and email providers, including server administrators, work hand in hand in creating a list of spammers. You can do your part too by marking unwanted emails as spam. This will then be reported and reviewed so that they can be added to the list.

Like what we have mentioned above, spam filters check the origin of every email. And if it is part of the blacklists, it will be forwarded to the junk mail.


Some spam filters have been excellently designed to analyze even the content of the email itself to determine if it is spam or not. This is how emails are categorized as well. However, there is a downside to this. Some legitimate emails may contain spammy sounding phrases, and that is why they end up in the spam folder.


Here are the different types of filters available these days:

1.      Header Filters - Review the data in the header and spot any altered or falsified information in an attempt to deceit the receiver of the email.

2.      Content Filters - Focuses on the content of the email and identify spam keywords as well as deceitful links.

3.      Permission Filters - Require the sender to be accepted by the receiver before they can send any message.

4.      Rules-Based Filters - This type depends on the user's specifications. A list of accepted senders can be created. Words in the subject line or body of the email can be specified too.

5.      General Blacklist Filters - Block all messages coming from all spammers included in the blacklist.

6.      Challenge-Response Filters - Ask the sender to enter a certain code before the message can be delivered.