What Is An Email Spam Filter And How Does It Work?
Email spam filters are specific types of software designed to analyze messages before they enter your inbox. These programs can work as part of your inbox or as an independent program hosted in the cloud or on your device.
Spam filtering software scans the sender’s address, subject line, attachments, and email body to determine if a message is “safe” or “suspicious.” Your email spam filter will assign each message a spam score based on what it finds. A “passing” score means the message can pass on to your inbox, whereas a “failing” score sends the message into a designated junk folder.
Additionally, some spam filters learn from you. For example, if you mark an email as spam, the spam filter will add content from that message to its spam filtering going forward. Similarly, if you send several letters from the same sender into your junk folder, the email spam filter software will start flagging all messages from that sender as spam.
Even if your email provider offers email filtering services, this may not be enough to protect your inbox from spam. Furthermore, spam emails can infect your computer with malicious software (malware). This malware can seriously damage individual computers or spread to an entire network of computers through a centralized server. Sometimes this malicious software renders computers unusable, whereas other times it steals personal data.
This is why you need an effective email spam blocker — it protects your computer and your data from hackers.
The Different Types Of Email Spam Filters Explained
As you can imagine, there are multiple types of email spam filter services available to both individuals and businesses alike. Most email providers, like Google and Microsoft, offer built-in spam filters, plus there are dozens of free and paid third-party email spam filter services out there, like SpamTitan and MailWasher.
While each of these gives you an effective email spam filter, not every solution works for every type of inbox. For this reason, it’s important to understand each type of email spam filter so you can choose the one best suited for your personal or business needs.
Built-In Spam Filters
If you use any type of major email provider, chances are they offer some sort of built-in spam filter. For example, the Gmail spam filter uses Google’s database of malicious links, keyword searches, and blacklisted sender addresses to filter out potential junk messages as they hit your inbox. If a message is deemed as a threat, it gets moved into a “spam” or “junk” folder instead of your inbox with the rest of the emails you receive.
While this may seem like an effective solution, it's not always the best option. Because most built-in spam filters use simple metrics to filter spam, they often falsely label items as spam or miss junk messages entirely. Furthermore, since many of these systems just migrate messages into a dedicated spam folder, there's still the potential for you to open malware or other harmful messages.
Free Third-Party Spam Filters
As previously mentioned, even the most secure email provider misses junk from time to time. Therefore, third-party spam filter solutions exist to bridge the gap between what built-in spam filters catch and what users actually need.
Believe it or not, there are actually many free spam filter services available for individual users. These spam filters often block junk messages and use a mixture of pre-established filtering rules alongside Bayesian filtering that learns your preferences. This means they do a much better job of filtering messages than the built-in settings within Gmail or other email services.
However, most free-to-use systems lack adequate features and customer support for enterprise-level clients and even some small business accounts. They also don't always offer integration with corporate email systems, which can cause extra work for IT departments.
Paid Third-Party Spam Filters
Obviously, the best spam filtering solutions are those which you pay to use through a third-party vendor. These types of solutions usually stop 99.9 percent of junk messages from ever hitting your inbox, plus offer advanced features like intuitive filtering, user behavior monitoring, and compatibility with any business software suite. Most importantly, these paid solutions usually offer other security features too, which means they keep your inbox (and your entire computer) safe.
For example, many spam filtering services that charge users prevent the installation of attachments on flagged messages, link clicking within suspicious emails, and other tactics that may result in email fraud. Paid email spam filter services also provide monitoring for outgoing messages, which can prevent hackers from using your email address or email server to send out malicious messages.
These extra security measures, along with the compatibility with G Suite or Office 365 make it worthwhile for businesses to invest in a premium email spam filter service.
The Most Effective Spam Filtering Services
While there are dozens of options out there for spam filtering, no two email spam filtering services are created equal. This is why we’re here to help you make an informed decision regarding which spam filtering service you should use.
Here are the 12 most effective spam filtering services:
- N-Able Mail Assure (formerly SolarWinds): best spam filtering accuracy
- Spam Bully: great Bayesian filter
- SpamSieve: great for Apple users
- Securence: best for small businesses and nonprofits
- SpamTitan: best for enterprise users
- MailWasher: best free version
- Comodo Secure Email Gateway: great for large message volumes
- SPAMfighter: great for non-English users
- Hornetsecurity’s Email Spam Filter and Malware Protection (formerly ZEROSPAM): great for Office365 users
- MX Guarddog: most affordable per email address
- MailChannels: great for rectifying email delivery issues
- Symantec Email Security.cloud: great for its advanced protection
1. N-Able Mail Assure
Price: from $1/mailbox/month with volume discounts available
N-able Mail Assure is a cloud-based email spam service that offers a unique value proposition for many MSPs and IT Pros working in SMBs. The product has flexible pricing options and offers over 99.9% spam filtering accuracy, business continuity, and email archiving.
N-able Mail Assure stands apart from its competitors because it is built on technology that is developed in-house. Whereas some other email security providers resell technology, N-able has full control over its tech stack and quickly responds to new email-borne threats. Since Mail Assure is also a cloud-based email filtering service, it’s easy for individuals and businesses to configure and deploy, regardless of the systems they use. It also uses SSL/TLS traffic encryption, seamless integration with Microsoft Office 365 and Outlook via an add-in and single sign-on.
- Over 99.9% spam filtering accuracy
- Flexible pricing options
- Seamless integration with Microsoft Office 365 and Outlook
Price: $29.95 annually
SpamBully is a relatively affordable email spam service at just $29.95 for a yearly subscription. It’s straightforward to install and intuitive to use, making it an accessible option for nearly any user. It offers detailed email information, phishing detection, spam blocking, message quarantine, and blocklist data.
While SpamBully offers a wide array of beneficial perks, one of its key features is its ability to learn what each user considers spam and adapt its settings based on your needs. The program will monitor your behavior over the first few weeks of use to determine how to filter spam in the future.
Unfortunately, one potential drawback of SpamBully is the fact that it is only available for Windows email clients, meaning Outlook, Live Mail, Outlook Express, and Windows Mail. However, for anyone using Outlook or Microsoft, this third-party email filter offers a robust suite of features that make it easy to keep your inbox clean and reduce the time you spend managing emails you aren’t interested in.
- Can recognize even sophisticated junk messages
- Uses monitoring to learn user behaviors
- Doesn’t work on mobile devices
Price: one-time purchase of $30
SpamSieve offers one of the most powerful and well-known spam filtering services for Mac and is compatible with operating systems as far back as 10.7, with older versions of the software available for machines at 10.2 or newer. SpamSieve also works with the iOS app, the desktop version can keep junk out of your mobile inbox if you use Apple Mail.
Like SpamBully, SpamSieve uses adaptive learning capabilities to change its behavior over time. Additionally, this spam email blocker integrates with your macOS Contacts App to ensure that messages from your trusted contacts are never accidentally marked as spam. Furthermore, you can customize your SpamSieve experience through settings and scripts.
Unlike some other spam filters on this list, SpamSieve works as a plug-in to your current inbox. This means you don’t need to open another application just to access your settings and functions for your spam filtering — you can just open your email client. Although it’s only compatible with macOS, SpamSieve connects to Apple Mail, Outlook for Mac, Airmail, and other popular macOS email clients.
For users who are skeptical of committing to a program without having tested it, SpamSieve offers a 30-day trial, during which users have access to the entire set of features. However, based on our testing, we believe SpamSieve is the best email filtering service for individual Mac users.
- Premium version available as a one-time purchase
- Free trial available
- Great for Apple Mail users
- Runs only on Mac computers
- No free version available
Price: Quote Required
Securence is a popular spam filtering service for small businesses, educational and governmental bodies, and enterprises. Interested parties can set up a 30-day free trial on their website, at which time they will receive a custom quote based on the size of their business and the scope of their needs.
One of the biggest benefits of Securence for businesses is the fact that it requires very little maintenance or upkeep once you work through the initial setup with your company email platform. Another impressive feature is that it doesn’t just block spam email, it also notifies users when messages are blocked or quarantined. The software also filters and reads mail logs, effectively flags junk and malware, and even stops phishing attempts.
However, one of the features of Securence that we found most beneficial for modern companies is its business continuity service, which ensures that your organization will maintain access to email even in the event of an unexpected loss of service. Avoiding downtime is more crucial than ever in such a connected time, and Securence makes that a top priority.
- Effective spam filtering
- Exceeds GLB and HIPAA security standards
- Offers email caching as part of its business continuity service
- Intended primarily for small businesses and enterprises
- Confusing admin panel
- Some false detections
Price: Quote Required
SpamTitan pledges to stop 99.9% of spam before it reaches your inbox, drastically reducing the time spent on managing your email accounts. Like Securence, SpamTitan provides a 30-day free trial to potential clients, including free technical support, after which interested users can seamlessly access their existing settings and information in the premium version.
Unlike other options on this list, SpamTitan includes two different antivirus protection mechanisms to ensure that nothing, even potentially compromising, ever reaches your inbox. It scans all parts of inbound messages, including links and attachments. Additionally, SpamTitan will scan and discover phishing email attacks, spear-phishing attacks, and zero-day attacks that may target your inbox.
SpamTitan combines machine learning and Bayesian analysis, which helps it work most effectively for you while also catching any new threats before you notice them. However, SpamTitan can be difficult to navigate, especially for less tech-savvy customers.
- Easy to set up
- Affordable monthly billing
- Allows whitelisting
- Enterprise-oriented email spam filters
- Not ideal for MSP
Price: Free (for single email address)
MailWasher claims a user base of over 8 million people, and it’s easy to see why so many have been drawn to its features and accessibility. In contrast to many other applications described above, MailWasher is the only spam email filter that offers an entirely free spam blocker in addition to a paid version.
Based on our testing, MailWasher offers the best free email spam filter for a single inbox. Regardless of which version of MailWasher you use, it will block spam before it reaches your inbox by previewing and deleting messages that seem suspicious. Additionally, the program scans for offensive content and filters out messages it deems “inappropriate.”
While many users are content with the features available as part of the free version of MailWasher, there are substantial benefits to upgrading, currently $49.95 per year. In addition to all free features, premium users can use MailWasher with multiple addresses and receive technical support and other capabilities.
- Free version available
- Works with all popular email services
- Filters out inappropriate content
- Confusing user interface
- Free version contains advertising
7. Comodo Secure Email Gateway
Price: Quote Required
Designed for enterprise users, Comodo Secure Email Gateway is an email spam filtering service that can handle large volumes of unwanted email messages. It relies on Comodo’s patented containment technology, which allows users to open attachments in isolated containers, where they are analyzed to determine whether or not they’re safe. Only when an attachment is considered to be safe is it allowed to leave the container.
Comodo Secure Email Gateway is a third-party spam filter available in the cloud, dedicated hosted cloud, and on-premises. All versions of this spam filtering solution offer many extra features, including full malware filtering, email classification, banner and plugin filtering, DoS attack prevention, and IPv6 support.
What really impressed us about Comodo’s spam filtering is its unique approach. Unlike other email filtering service options, this app analyzes files for threats before they arrive in the inbox, and then sandboxes them. In other words, all attachments are placed in a protected environment to catch any malicious activity or phishing attempts before they happen. By doing this, Comodo Secure Email Gateway helps you ensure you can open any and all attachments without any fear of what they may do to your system. Furthermore, the program’s advanced filtering methods can help you easily trash or sort emails based on sender, attachment size, or keywords within the email.
While Comodo offers a powerful email spam blocker, its software is best suited for enterprise-level users.
- Proven enterprise email spam filter
- Comodo AV and Valkyrie integrations
- Free trial available
- Best suited for enterprise users
Price: starts at $29.99
SPAMfighter is a capable spam filtering solution for Outlook, Outlook Express, Thunderbird, Windows Mail, and Windows Live Mail users. It runs only on Windows XP, Windows Vista, Windows 7, and Windows 10. This spam filtering solution has been translated into most major languages, including English, Chinese, and German, which makes it an ideal solution for international businesses.
Like a guard, SPAMfighter checks all new emails that arrive in your inbox and tests them to determine if they are legitimate. When SPAMfighter finds an email that's not legitimate, it automatically removes it from your inbox and moves it to the junk folder. Should a spam email message slip through, you can simply mark it as spam with a single click, which automatically removes it from all other community members.
Furthermore, SPAMfighter offers live statistics for all messages, including your total inbox volume, spam-to-message ratio, and the total number of blocked spam attempts made in a specific period of time. These tools can be highly useful for businesses, but also individuals who are curious about the amount of junk they receive.
- Simple user interface
- Partnership with Microsoft
- Works only on Windows
- Compatible only with desktop email clients
9. Hornetsecurity’s Email Spam Filter and Malware Protection
Price: Quote Required
Hornetsecurity’s email spam filtering service (formerly ZEROSPAM) stands as a top-tier defense against cyber threats via email. Boasting a 99.9% spam detection and 99.99% virus detection rate, it's recognized as one of the best email spam filter services on the market. The service effectively shields mail servers from DDoS attacks and phishing emails, utilizing multi-layered email spam filter mechanisms that block the bulk of spam emails upon arrival. This ensures that the quarantine remains uncluttered and user-friendly.
Additionally, the service comes equipped with intelligent protection mechanisms distributed across multiple data centers, safeguarding legitimate mail traffic even under the onslaught of large-scale DDoS attacks and waves of spam. With a fully managed solution, Hornetsecurity handles the management, operation, and monitoring, ensuring consistent performance and an impressive 99.99% uptime. For IT administrators, the system is intuitive, with essential information easily accessible and settings that can be quickly configured.
- 99.99% virus detection
- Tailored for Microsoft 365
- Comprehensive security & backup features
- Positive customer testimonials
- Pricing available only after registration
- Mainly targets enterprise customers
10. MX Guarddog
Price: $0.25 per email address per month
MX Guarddog is a cloud-based email spam filter that serves as the first line of defense against junk, computer viruses, malware, phishing emails, spoofed undeliverable notices, and Denial of Service attacks (DoS). When MX Guarddog detects a suspicious email, it moves it to quarantine and, at the same time, sends you a notification so you can decide what to do with it.
MX Guarddog uses TLS-based encryption and Perfect Forward Security (PFS) to keep your emails secure, and it also offers 99.95% SLA, which means that it shouldn’t be unavailable for more than a little over 4 hours per year, making it very dependable.
You can try MX Guarddog for free for 30 days to see how it works. After the free trial period ends, MX Guarddog charges $0.025 per email address per month. So, if you want to use this spam filtering service with 100 email addresses, your monthly cost will be $100.
- Affordable pricing
- Free trial available
- Great reputation
- Strongly geared toward enterprise users
- Not user-friendly
Price: Starting at $79.99/month
Businesses who offer web hosting or manage multiple email domains need a robust way to stop spam emails for both inbound and outbound mail. That’s exactly the solution MailChannels offers — protection from unsolicited emails and more for enterprise-level users.
One key benefit of MailChannels is the fact that it uses behavior analytics and response analytics to provide multi-layered spam, malware, and phishing protection. Also, unlike other spam filter programs, this service provides detailed message logs so users can easily figure out why a message was blocked or quarantined.
Unfortunately, MailChannels is not an inexpensive solution. Since it is made for enterprise users, you can’t obtain a plan for less than $79.99/month. That being said, this rate is actually quite affordable for users who manage inboxes that send and receive thousands of messages per month.
- Supports high-volume email accounts
- Provides multi-layered protection
- Provides detailed logs for messages
- Strongly geared toward enterprise users
12. Symantec Email Security.cloud
Price: Quote Required
Symantec Email Security.cloud is a cloud-based email security solution that offers many advanced features for users who need high levels of protection. Although our research showed this solution costs more than some other options, it may be worth it if you need what it offers.
One of the major selling points for Symantec Email Security.cloud is that it is programmed to handle advanced email attacks and protect against data leaks. If your email account ever contains financial documents or similar sensitive information, this could be exactly the spam filter you need. We also noticed that it provides security against phishing and spear phishing attacks.
Although most spam blockers will let you add individual email addresses to a black list, Symantec Email Security.cloud lets users lock IPs and Domains as well. Furthermore, you can find detailed reports within the app’s built-in dashboard, meaning you can look for patterns or make changes as needed based on the data you see.
- Comprehensive protection for Office 365, G Suite, and on-premises
- Features Email Threat Isolation against risky links and attachments
- Integrated cyber defense exchange simplifying product integrations
- Security awareness training via Phishing Readiness capabilities
- Comprehensive data loss prevention capabilities
- Integration with many features may increase setup complexity
- Detailed pricing and package specifications not provided upfront
How Clean Email Can Provide Even More Inbox Protection
Spam filtering can do a lot to free your inbox from unwanted and malicious messages. However, it doesn’t help you fully achieve Inbox Zero. Luckily, Clean Email is designed to simplify the decluttering process for your overloaded mailbox and help you maintain a clean inbox by automating email cleaning tasks as you go.
While Clean Email is not an email spam filter service in and of itself, it does offer many tools that can help you stop spam messages from filling your inbox. For example, the Unsubscriber tool can help you pause subscriptions, remove all messages from a certain sender except the newest one (‘Keep Newest’ feature), send unsubscribe requests on your behalf, and more.
Furthermore, you can block messages from senders or entire domains, which can help you avoid multiple hits from malicious sender addresses.
Then, you can use the Auto Clean feature to apply rules and actions to any message as it arrives in your inbox. This means you can automatically set emails to go into specific folders, archive them, or delete them entirely based on factors you decide. This can save you hours of work, and can be applied to messages already in your inbox as well as ones that may arrive in the future.
The Privacy Monitor feature can check for known data breaches and security incidents. If your account was compromised in any data breaches, you will be suggested to take immediate actions such as changing your password or enabling multi-factor authentication. This is above and beyond what any email spam filter will do, and it’s an important step to help protect your inbox and, ultimately, your identity.
With a free account, users can manage up to 1,000 emails, which Clean Email will automatically group based on its analysis of each message. Besides, you can test the premium features during the 14-day trial as well as unsubscribe from up to 25 subscriptions for free. Upgrading to a premium account allows for unlimited email management and a wider range of features, including managing email subscriptions and setting up rules for the automatic analysis of future messages.
Wondering to get more tips on how to protect your mailbox from spam? Check out our guides on how the iPhone email filter works and how to filter emails in Apple Mail.
Email Spam Filter Software - FAQs
How does an email spam filter work?
Spam filters are tools programmed to identify unwanted or dangerous messages before they hit your inbox. In most cases, these tools scan specific parts of any message, from the sender address and subject line to the contents of the message itself. Then, based on what it finds, the filter decides if the message passes or fails — and places it in the appropriate place based on the score.
How do I create a spam filter for my email?
If you’re unsure how to stop spam emails from hitting your inbox, you can usually create filters and block certain addresses from your email client’s settings menu.
How do I bypass spam email filters?
If you are using Gmail and want to bypass spam email filters, first you must click on the Settings gear. Then, navigate to “Advanced Settings.” Go to “Spam,” then click “Add Another.” From there, check the “Bypass spam filters” box for any addresses that you want to show up in your regular inbox.
Is there a spam blocker for email?
While most built-in spam filters do not block emails entirely, there are both free and paid email spam blockers available online. Several of these services are mentioned above.
What is the best email spam filter?
There are many email spam filtering options out there, but not all of them meet the needs of every user. To find the best email spam filter for you, it’s best to outline your needs and desires in a filter, then carefully research options that meet your criteria.
How do I set up spam filters on my iPhone?
If you want to set up an iPhone email filter, you must first open the Mail application. Find a message from one of the senders who you want to block. Swipe left on the message. Tap the option for “More.” A pop-up menu will appear. Tap on the “Mark” option, then tap “Move to Junk.” You can also select multiple messages and use the technique to block a variety of senders. This will send all messages from these addresses to your spam or junk folder.
What is the best spam filter for Outlook?
Most email spam filter services are compatible with Outlook. Some options include N-Able Mail Assure, SpamBully, SPAMfighter, and MailWasher.