What Are Email Filters? And How They Work to Stop Spam

Email filters help detect spam, viruses, and malware before they land in your mailbox, which makes them a vital part of cybersecurity. Email filtering services sift through incoming and outgoing emails to classify and categorize them.

Although most spam emails are easy to spot, some can be nearly undetectable. Many cyberattacks start with a spam email, which is why email filters are crucial.

You need a corporate email filter capable of deflecting the vast majority of attacks to prevent spam. Smart spam detectors save time and energy and keep your organization protected. Learn how they work, why you should use them, and how to get one.

An email spam filter analyzes emails for common red flags that indicate spam or malicious content. If the filter detects a red flag in an email, that email is separated into a spam folder or blocked entirely.

Common signs of spam emails include:

• Bad IP Addresses: Emails coming from IP addresses with a bad reputation may be flagged and labeled as spam.

• Poor Domain Reputation: Emails sent from domains previously associated with spam are likely to trigger an email filter.

• Bulk Emails: High sending rates from a sender can indicate that an email is spam.

• Suspicious Language: Emails containing words like "free" and "refinance" can tip off a spam filter.

• Links in the Email Body: Spam filters can flag URLs, especially if they’re shortened or redirected.

Email filters can scan and filter both incoming and outgoing emails. The latter is particularly important in identifying a compromised account, which could lead to a surge in outgoing spam emails.

The process of filtering spam is usually conducted automatically by an SMTP (Simple Mail Transfer Protocol) server. SMTP servers reject, redirect, or quarantine an email depending on the contents and their anti-spam techniques.

Most mainstream secure email providers already have these filters. Gmail, for example, categorizes emails as spam, promotional, or social based on the content and the sender’s reputation. Outlook automatically filters spam emails, and users can easily create custom rules to further categorize emails.

Current email spam filtering services are more advanced than ever before, so most spam emails never successfully make it into your primary inbox. However, modern cyberattacks are built to outsmart standard email filters. Phishing emails, for example, often rely on targeted social engineering, rather than mass sending. Sophisticated phishing attacks don’t share the characteristics of common spam emails, so they can easily slip past traditional email spam filters.

Email spam filters use various techniques and technologies to identify and block unwanted emails. Here are the spam filters you’re likely to encounter:

• Content: A content filter analyzes the text inside an email. It uses this information to decide whether something is spam or not. Specific trigger words will lead to the email being quarantined.

• Block List: These filters block emails based on the sender. Any address that's flagged as a spam email sender will have its emails quarantined immediately. With a business spam filter, you can also customize your block list.

• Header: Header filters examine the header of an email. They search for inappropriate sources and IP addresses to prevent previously flagged senders from simply creating new email addresses.

• Language: Some email filters check for foreign languages to prevent communications in languages the recipient is unlikely to understand.

• Rule-Based: A rule-based filter allows you to customize your filters by applying specific rules. For example, if there’s a specific word or phrase within the body of an email, you could instruct your filter to automatically send it to spam.

• Bayesian: A Bayesian filter learns your preferences by monitoring the emails you send to your spam folder. It observes what you mark as spam and attempts to decipher the trends and patterns so it can increase its accuracy.

All these filters serve a purpose. And every premium spam blocker for email will likely include each of the above filters bundled together.

Your built-in email filter through Microsoft or Google probably catches plenty of spam, but spam emails often slip through the cracks. Abnormal can catch the spam attacks that native email security misses using advanced AI and machine learning technologies.

Abnormal uses AI to analyze not just the content of emails but also the context and relationships within your organization.

Here are some ways Abnormal flags email as spam:

1. Unidentified Vendor: The email came from an unidentified vendor without a company name.

2. Generic Content: The email was generic, meaning the recipient's name and employer weren’t mentioned, which can indicate the email was sent to numerous addresses across multiple companies.

3. Multiple Recipients: The email was sent to multiple people within the same company.

Abnormal constantly refines spam filters at an individual level. What’s spam for one user may not be spam for another, based on their own preferences.

By analyzing how each user interacts with emails, Abnormal creates separate safe and block lists per inbox. See our spam filter in action by requesting a demo.

Why should you invest in a business spam filter? There are several benefits to choosing a cutting-edge spam filter service for your organization, including:

• Increase employee productivity

• Reduce the odds of a cyberattack

• Automate your spam filtering

• Streamline your email inbox

The best part is that a strong cybersecurity solution doesn’t have to cost a huge amount of money to take advantage of state-of-the-art online spam filtering.

When combined with email security that stops advanced email attacks, you can protect your organization from the daily nuisance of spam, as well as the modern threats that lead to more serious financial and reputational damage.

Email spam filters assess incoming (and sometimes outgoing) emails for spam content. They look for known red flags like sender reputation, trigger words, spoofed IP addresses, and suspicious links to identify spam. Advanced filters leverage artificial intelligence and machine learning to adapt to new spam tactics and improve detection rates.

While spam may seem harmless, it's at best a productivity killer and at worst a potential path for a devastating cyberattack. Spammers continuously refine their techniques, using tactics like phishing and social engineering that may bypass standard filters. That’s why some spam still slips past native email filters and into your inbox.

Abnormal's email security service goes beyond standard email filters in blocking spam. By leveraging advanced machine learning and behavioral analysis, Abnormal can detect and prevent sophisticated email threats that others miss. If you want to stop spammers in their tracks, request an Abnormal demo.