What is a spam filter and how does it work?

What is a spam filter and how does it work

Every day, billions of unwanted emails including advertisements, scams and phishing attacks are sent across the internet. Fortunately, most of these never reach your inbox. This is thanks to spam filters.

Different email service providers, such as Gmail and Yahoo Mail, come with built-in spam filters that utilize advanced algorithms to combat unsolicited emails.

In this article, we explain what a spam filter is, how it works and what types of filters are most commonly used to block email threats.

Introduction to email spam filters

Email spam filters are a crucial component of email management systems, designed to detect and prevent unsolicited, unwanted, and malicious emails from reaching a user’s inbox. These filters use various techniques, including content analysis, header analysis, and machine learning, to identify spam emails and block them from entering the inbox. By using spam filters, users can reduce the amount of unwanted emails they receive, protecting themselves from potential threats such as phishing, malware, and other types of cyberattacks. Effective spam filters can also help improve the overall email experience, reducing clutter and increasing productivity.

To better understand the risks, learn how phishing works and explore how malware spreads through email.

What is a spam filter

A spam filter is a tool that automatically detects and blocks unwanted emails. It can be a piece of software, a physical device or a cloud-based solution. Spam filters analyze incoming and outgoing emails to identify messages that are irrelevant, dangerous or malicious.

When an email is received, the spam filter evaluates it using algorithms and predefined criteria. Factors like sender reputation, trigger words, and spoofed IP addresses are analyzed to determine if the email is suspicious. If the email seems suspicious, it is blocked or sent to the spam folder instead of the main inbox.

Types of spam filters

There are different types of spam filters designed for various needs depending on whether they are used by individuals, businesses or large organizations.

Email software often integrates spam filtering solutions to enhance the security of users' inboxes.

Gateway spam filters

A gateway spam filter is installed at the entry point of a network. It scans incoming emails before they reach users inside the network, scrutinizing IP addresses, particularly those with a bad reputation, to prevent spam emails from reaching users. These filters are typically hardware-based and placed on a local server to act as a security layer between the internet and the internal system.

Hosted spam filters

A hosted spam filter is a cloud-based solution managed by an external provider. It filters emails before or as they enter a network. These filters can be updated regularly and scaled easily, making them ideal for businesses. They are often offered as part of a subscription service.

Desktop spam filters

Desktop spam filters are installed directly on a user’s computer. They allow the user to customize how emails are filtered. This is a good option for individuals or small teams who need more control over which messages are allowed or blocked. Additionally, desktop spam filters enable users to create custom rules to further categorize their emails, tailoring their email management to personal preferences and unique spam characteristics.

Advanced filtering techniques

Advanced filtering techniques, such as Bayesian filters and machine learning algorithms, can be used to improve the accuracy of spam filters. These techniques involve analyzing the content and behavior of emails to determine whether they are spam or legitimate. By using advanced filtering techniques, spam filters can reduce the number of false positives and false negatives, providing a more effective and efficient way to manage spam emails. Additionally, advanced filtering techniques can help to detect and block new and emerging types of spam, such as phishing and spear-phishing attacks.

How spam filters work

Spam filters use several different methods to identify and filter out unwanted emails. Below are the most common techniques.

Content filtering

Content filtering examines the content of the email including the header and body. The header contains metadata such as sender information and the email’s path to the recipient. The filter checks for inconsistencies or suspicious signs in this data.

The body of the email is also analyzed for spam-related content such as certain keywords, patterns or links that are often used in phishing or scam emails. Additionally, content filters identify malicious content that can infect computers with malware, further safeguarding users and improving the reputation of email services.

Rule-based filtering

Rule-based filters rely on specific rules defined by the system or the user. These rules might block emails from certain addresses or domains, or target emails from specific senders by analyzing information such as the domain or sender's name, or flag messages containing specific phrases or attachments. When an incoming email matches a rule, it is automatically blocked or sent to spam.

Bayesian filtering

Bayesian filters are adaptive and use statistical methods to learn from user behavior. When a user marks a message as spam, the filter learns from its characteristics and creates specific rules for filtering future emails from the same sender. Over time, the filter becomes better at identifying similar emails and blocking them before they reach the inbox.

Benefits of using spam filters

The benefits of using spam filters are numerous, including reducing the amount of unwanted emails, protecting against potential threats such as phishing and malware, and improving the overall email experience. By using spam filters, users can reduce clutter and increase productivity, as well as protect themselves from financial and reputational damage. Additionally, spam filters can help to improve the reputation of email providers by preventing malicious emails from getting through, and can also help to protect valuable assets, including workstations, servers, and other elements of a network.

Spam filters vs malware filters

Spam filters and malware filters often work together but serve different purposes

• Spam filters block unwanted or irrelevant emails such as promotions or phishing scams

• Malware filters scan email content and attachments for harmful software such as viruses or ransomware

Modern email security systems usually include both spam and malware protection for full coverage.

Most used spam filters

• Exchange Online Protection 47 percent

• Proofpoint SEG 15 percent

• Mimecast SEG 12 percent

• Cisco IronPort 12 percent

• Google Mail 11 percent

• Symantec MessageLabs 3 percent

• Trend Micro HES 3 percent

• Barracuda Email Security 2 percent

• Forcepoint Cloud 1 percent

• FireEye ETP Cloud 1 percent

These spam filtering solutions include various tools and programs designed to detect and prevent unsolicited and harmful emails from reaching users' inboxes.

Most used malware filters

• Exchange Online Protection 50 percent

• Proofpoint SEG 16 percent

• Mimecast SEG 12 percent

• Google Mail 11 percent

• Sophos AV 10 percent

• McAfee AV 2 percent

• Barracuda Email Security 2 percent

• Symantec MessageLabs 1 percent

• Forcepoint Cloud 1 percent

• FireEye MX 1 percent

These solutions employ various mechanisms and technologies in email spam filtering to protect users from unwanted, potentially harmful emails, including spam, malware, and phishing attacks.

Why spam filters are essential

Whether you are managing a personal inbox or protecting a large organization, spam filters play a crucial role in keeping email communication safe and secure. Effective spam protection is essential in safeguarding organizations from various email threats. Spam filters and blockers reduce the risk of phishing, scams, and malware while saving time and resources.

With cyber threats becoming more advanced every year, using a reliable spam filter is one of the most important steps you can take to protect your digital environment.