How does email spam filtering work?

How does email spam filtering work?

Spam is a nuisance and productivity drain for most, if not all, small- to mid-sized businesses (SMBs). Employees spend around five minutes a day dealing with unsolicited and unwanted emails — seemingly inconsequential minutes that can add up to hours, days, or even weeks of lost productivity. However, these productivity losses are minor compared to the damages that can be caused by phishing attacks, malware infections, and other dangerous cyberthreats.

Without effective email spam filtering, a considerable number of harmful messages and attachments will reach end users. And all it will take is for one employee to simply open or respond to a malicious email for a catastrophic data breach to occur. That’s why businesses need to shore up their security defenses — and having a robust email spam filter is nonnegotiable.

What is a spam filter?

A spam filter is a piece of software designed to distinguish emails with unwanted or dangerous content from genuine correspondences. Once it identifies spam or potentially malicious emails, it blocks them from reaching the target user’s inbox.

How does a spam filter work?

A spam filter uses predefined rules or algorithms to parse email messages and look for distinguishing features that are common to spam. Here are the most common types of spam filters and how they work.

1. Header filter

A header filter analyzes the elements of an email header to see if it came from an illegitimate source. For example, it checks the Internet Protocol (IP) address of the sender against those that spammers are known to use. A header filter can also look for information that indicates the email is just one copy of many emails sent simultaneously to an indiscriminate list of recipients.

2. Content filter

A content filter examines the information contained in an email to decide whether or not to mark it as spam. Typically, spam emails offer deals, promote explicit material, or tap into human emotions, feelings, and desires — which is why they often carry predictable content.

A content filter may search for words associated with these objectives. For instance, spam emails that offer deals often mention the terms “discount,” “limited time,” or “offer.” Multiple uses of the target words triggers the filter.

A content filter may also check an email for inappropriate or offensive language that could indicate explicit content. In some cases, an attacker may use sexually explicit material to lure users into clicking on malicious links or downloading malware-ridden attachments.

3. Blacklist filter

A blacklist filter blocks emails from senders that are known to send unsolicited emails. Many blacklists — lists of IP addresses or domains identified as sources of spam — are updated in real-time since spammers regularly change their email addresses.

You can even create your own blacklists to protect your organization’s interests. For example, you could list down headhunters seeking to attract your current employees and block all correspondences from them. You could also blacklist email addresses that send sales offers and promotions that could distract employees from getting work done.

4. Rule-based filter

A rule-based filter lets you establish specific rules that can be applied to all incoming emails. If an email’s content or origin matches at least one of the criteria, it’s automatically sent to your spam/junk folder. For instance, you can set a rule to look for certain words or phrases in the body of an email, and if these are present, then the message is marked as spam.

You can also use a rule-based filter to target specific senders. That is, you can set it up to analyze the sender’s name or domain information to determine if the email indeed came from the purported sender.

5. Bayesian filter

A Bayesian filter is perhaps the most efficient type of spam filter, as it can learn your preferences by examining the emails that you consider as spam. It studies the content of the emails you actively mark as spam, recognizes patterns, and then sets up rules accordingly. These rules are then applied to all future incoming emails.

A good spam filter does not only block productivity-draining emails, but it also offers robust protection against email-based threats. For an enterprise-level email security solution at an SMB-friendly price, try Kortek Solutions’ Email/Spam Protection. Contact us today to learn more.