Best Anti Spam Software

It is important to spend some time assessing the best anti spam software solutions on the market to ensure they are suitable for your business and will give you the required level of protection against email-based threats such as phishing, malware, ransomware, and botnets.

Not all anti spam solutions are equal. Some anti spam and anti phishing solutions, even those from some of the best-known brands in cybersecurity, fail to live up to expectations. Some businesses only discover that once they are tied into a contract, which may last for 1-3 years. Upfront research can save a lot of headaches.

While many solutions appear to provide all the features and functions that you are likely to need, many fall down because they are overly complicated to use. If a solution is hated by your IT department, staff will avoid using the solution as much as possible. If tweaks are not performed and the solution is not properly managed, malicious emails are likely to sneak through and reach end users’ inboxes. That could easily result in a very costly data breach.

There are several factors that should be considered before you commit to an anti-spam solution. In this article we explain some of the most important features of anti spam software to look for. We hope that this article will speed up the decision process and help you to choose the best anti spam software solution for your business.

How Does Anti Spam Software Work?

Before explaining the main features of the best anti spam software solutions, it is worthwhile explaining how anti spam solutions work.

Once implemented, all incoming emails will be directed through your chosen solution. That could be a hardware-based anti spam appliance, a software-based virtual appliance, or a cloud-based spam filter. The solution will perform several front-end tests that will identify the majority of spam and malicious emails and block those messages.

One of the most important front-end tests is to compare the sender’s IP address against a Realtime Blackhole List or RBL. An RBL is a maintained list of IP addresses that have been previously used for spamming or sending malicious messages. If an IP address is on an RBL, all emails from that IP address will be treated as suspicious and will be blocked by your anti spam service.

Email attachments will be scanned for malicious code using a signature-based detection method. Anti-virus engines in the solutions will identify all known malware variants and will neutralize those threats. Checks will also be performed on the content of the messages. The solution will search for the common signatures of spam, such as spelling and grammatical errors, overuse of certain keywords, and excessive or malicious hyperlinks. Messages will then be assigned a spam score. The higher the score, the greater the likelihood that the message is spam or malicious. Administrators can set the threshold score on the best anti spam software depending on their organization’s level of risk tolerance. Any message that exceeds the threshold is marked as spam and is quarantined or rejected.

Using these spam detection methods, the best anti spam software will block between 98% and 99% of incoming spam email. However, since all it takes is for one malicious email to make it past those defenses for a costly data breach to occur, detection rates need to be higher. That will require more advanced spam detection techniques.

Key Features of the Best Anti Spam Software Solutions for Business

RBLs may be the core component of many anti-spam software solutions, but they are only useful for blocking emails from known spam sources. Emails from new IP addresses that have not previously been used for spamming will pass straight through the filter. Cybercriminals often test their messages to make sure they do not trigger content-based and keyword-based spam filtering controls in commonly used email services such as Office 365. To improve detection rates further and block more than 99.9% of incoming spam and email threats, more advanced detection methods are necessary.

Bayesian Analysis

The best anti spam software uses a technique called Bayesian Analysis to perform a much deeper assessment of message content to identify heavily obfuscated malicious messages. A linguistic algorithm is used to assess words and phrases and compare them to messages previously categorized as spam. This technique allows the spam filter to ‘learn’ and get better over time.


Incoming emails that are clearly spam or malicious will be blocked using the above techniques, but many emails fall into a ‘grey area.’ This is where greylisting comes into play. Greylisting involves sending a request to the originating server asking for the message to be resent. This is not used on all incoming emails, only those where further clarification is required. Since email servers used for spamming are usually busy on huge spam runs, there will be a delay in resending the message – if the message is resent at all. The delay is an indicator of whether the server is spamming.

DMARC Email Authentication

Domain-based Message Authentication, Reporting and Conformance (DMARC) is an email authentication protocol that is used to determine whether the sender of a message is authorized to use a particular domain. A company will set their DMARC record and all email servers can check emails against that record to make sure that the sender is authorized to use the domain. DMARC is one of the most effective ways of blocking email impersonation and Business Email Compromise (BEC) attacks.


SURBL/URIBL filtering involves scanning incoming messages for embedded hyperlinks to malicious or suspicious web pages. When a URL is identified as being used for phishing, malware distribution, or other malicious purposes, the URL will be added to a blacklist. If that URL appears in any further phishing emails it will be blocked. This is an essential technique for blocking phishing emails.


Sandboxing is an additional layer of protection against malware and ransomware. AV engines will identify known malware, but not brand new – zero-day – malware. This is where the sandbox comes into play. Suspicious email attachments are examined in a totally isolated environment for command and control server callbacks and other malicious actions.

Outbound Email Filtering

Not all spam email originates from outside the company’s email system. Rogue employees may use a company email account for conducting their own malicious campaigns and hackers may succeed in compromising an email account in a phishing attack. That account is then often used to send further phishing emails. With outbound email filtering, lateral phishing attacks and BEC attacks can be identified and blocked. Without outbound filtering, organizations will find it harder to identify compromised accounts and malicious email activity from within the company.

Make sure that your chosen solution incorporates all the above features and you will be able to block in excess of 99.9% of spam and keep your email system free of business-destroying malware and ransomware.

Selecting the Best Anti Spam Software

Price is often a good gauge of quality, but it is not an ideal way of choosing the best anti spam software for your business. There are advanced anti-spam solutions on the market that provide the same, if not greater, protection against email threats at a fraction of the cost of the most expensive solutions.

The best anti spam software providers are confident in their products and offer potential customers free trials. The trials allow you to test the full product in your own environment to see how effective it is at blocking spam and how easy it is to use. Independent review sites are also useful as they will let you see feedback from actual users of the product. You can then make an informed decision about the best anti spam software solution for your business.


How do spam filters work?

Spam filters use blacklists of known spammers, check the reputation of IP addresses, and analyze the email headers and content and score each email based on the probability of it being unsolicited, unwanted, or malicious. Administrators can set spam tolerance thresholds. If the score exceeds the threshold, the message will be quarantines, rejected, or deleted. Antivirus engines also check for malware in attachments and embedded hyperlinks are assessed.

What are the most important features of spam filters?

One of the most important features of a spam filter is greylisting. Greylisting involves rejecting a message and requesting the email be resent. Since the email servers of spammers are usually too busy on spam runs to respond, the delay is a good indicator of whether a message is genuine. Machine learning mechanisms are also important. They allow the spam filter to learn from previous classifications and predict whether new messages are legitimate or spam.

Do I need multi-factor authentication if I have a spam filter?

A spam filter is the first line of defense against phishing. Typically spam filters block in excess of 99.9% of phishing emails but some will be delivered to inboxes and employees may respond and disclose their login credentials. It is therefore important to implement multi-factor authentication for email to ensure that stolen credentials cannot be used to access corporate email accounts.

How can I improve the Office 365 spam filter?

The spam filter provided with Office 365 only provides a basic level of protection against spam, phishing, and malware. The best way to improve spam and malicious email detection rates and block more threats is to layer a third-party spam filtering solution on top of the Office 365 spam filter.

How much does an advanced spam filter cost?

An advanced spam filter that will block in excess of 99.9% of spam and phishing emails, 100% of known malware, and zero-day threats starts at a cost of around $12 per user, per year. Before committing to a purchase, take advantage of any free trials to evaluate a solution in your own environment.