Best Spam Filter for Outlook

Microsoft Outlook is a popular email client, but many businesses have reported receiving excessive volumes of spam in their inboxes which has led them to search for the best spam filter for Outlook. Fortunately, improving spam filtering for Outlook is relatively straightforward.

Outlook is commonly used with Microsoft Office 365, although other mail services can also be connected to Outlook. As with any email service, users of Outlook must deal with spam email, phishing and other email threats. Microsoft does provide a basic spam filtering service through Exchange Online Protection (EOP), but it is not sufficient to protect against advanced email threats.

A more advanced level of protection is available to Office 365 Enterprise E5 customers in the form of Advanced Threat Protection (APT). APT can also be added to other subscription plans for Outlook to improve protection against advanced threats such as spear phishing and zero-day malware.

If you want to improve the spam filter for Outlook, you will no doubt want to evaluate Microsoft’s solution and third-party Outlook spam filters. To help you whittle down the list of anti-spam service providers and find the best spam filter for Outlook, we have listed some of the most important features of spam filters for Outlook.

If an Outlook spam filter has these features, it will help you to block more spam and email threats and better protect your email system and network.

Why is a Spam Filter for Outlook Necessary?

Microsoft’s basic level of protection, EOP, does offer a reasonable level of protection against spam and unsophisticated phishing attacks. Users find the majority of spam and malicious messages are blocked and do not reach inboxes. However, a significant percentage of phishing emails bypass EOP controls and are delivered to end users.

One of the problems is Office 365 users are targeted by cybercriminals. A company using Office 365 has this broadcast through its MX record so cybercriminals can identify Office 365 users and target their campaigns accordingly. Cybercriminals can test their own Office 365 accounts to see if their carefully crafted messages bypass EOP defenses and arrive in inboxes. According to a study conducted by Avanan, around 25% of phishing emails reach EOP-protected Outlook inboxes.

The advanced anti-spam service for Outlook provides a much greater level of protection than EOP. Business users therefore need to pay for APT or use a third-party anti-spam service if they want to reduce the threat from phishing and malware to a reasonable and acceptable level, but which is the best spam filter for Outlook? APT or a third-party solution?

Features of the Best Spam Filters for Outlook

The best spam filters for Outlook incorporate extensive front-end checks for all incoming emails to determine the likelihood of a message being spam or malicious. The most advanced third-party spam filters for Outlook incorporate the features listed below. These ensure virtually all spam is identified and prevented from reaching inboxes, while advanced anti-malware features ensure that emails containing infected attachments or malicious code are quarantined or deleted.

The following features are not present in EOP but are included in many third-party spam filters for Outlook to ensure greater protection of the email system.

  • Dedicated Real-Time Blacklists (RBLs): RBLs are lists of IP addresses known to be used for spamming and malware distribution. The use of multiple RBLs ensures spammers are identified faster.
  • Greylisting:The process of rejecting messages and requesting they be resent. The time delay is an indicator of whether the originating server is being used for spamming.
  • Data Loss Protection: Data loss protection measures can be implemented to create custom policies that delete, redirect, or bounce emails that breach certain user-set rules.
  • Multiple Antivirus Engines: Multiple anti-virus engines and threat intelligence are combined to improve malware detection rates. If one AV engine fails, a secondary engine will ensure malware is still blocked.
  • Advanced Malware Protection: Predictive techniques, Bayesian analysis, heuristics, and machine learning are used to improve detection rates for zero-day malware. Sandboxing may also be included. This allows deep analysis of suspicious attachments for malicious actions.
  • URL Scanning: The scanning of all embedded hyperlinks in real-time against blacklists to identify URLs used for malware distribution, phishing, and other online scams.
  • Customizable policies:The ability to set custom policies for individual users and departments. Spam thresholds can be set for different mailboxes. Departments that are targeted by phishers (HR, accounts, C-Suite) can have more aggressive controls set.
  • DMARC authentication–Authentication of emails to make sure the sender of an email is authorized to use that domain. This is an important measure to protect against email impersonation and BEC attacks.

With these advanced spam and malware detection methods, the best spam filter for Outlook will block in excess of 99.9% of spam email, 100% of known malware, and zero-day threats and will have a low false positive rate.

What is the Best Spam Filter for Outlook?

Many companies claim to offer a top spam filtering service that can be seamlessly applied to Outlook to block phishing emails, malware, ransomware, and keep inboxes free of unsolicited, bulk email. These spam filtering services are applied on top of Outlook and augment its spam filtering capabilities. They provide much better protection than EOP and an equivalent, if not greater level of protection as APT at a more reasonable price point.

Cost will be one of the main considerations for SMBs looking for a spam filtering service for Outlook. Keeping costs down is important, but businesses need to make sure that opting for a lower cost solution will not have a negative impact on their security posture.

Businesses should therefore compare metrics such as spam catch rates, false positive rates, malware detection efficiency, and speed of processing incoming emails. These figures can be checked through third party review sites. VirusBulletinshould be checked to find out how effective an Outlook spam filter is at blocking malicious messages and review sites such as G2 Crowdshould be checked to obtain feedback from companies that have already signed up to what they hoped was the best spam filter for Outlook. These sites will give you a much better idea about how easy the solution is to use, manage and maintain.

Best Spam Filter for Outlook FAQs

Is Exchange Online Protection really that bad at detecting spam?

In 2013, Microsoft Outlook´s Cloud Business Development Manager – Benoît Roumagère – acknowledged that 2% – 3% of unwanted and unsafe emails avoid being detected by EOP. A subsequent test conducted by AV-Comparatives in 2016 rated Microsoft Outlook the worst performing of ten spam filters, after it detected just 89.87% of sophisticated spam emails. So, yes. It is really that bad at detecting spam.

How do third-party spam filters for Outlook stop phishing emails?

URL scanning engines compare embedded hyperlinks against URIBL and SURBL block lists that include top level domain names and websites that have recently appeared in spam and phishing emails. The URL scanning engines can also be configured to prevent users visiting websites that hide their true identity behind a proxy server of the whois privacy feature.

Why would you apply different spam thresholds to different users/departments?

While it might appear practical to apply optimal spam thresholds universally across an organization, by applying the same optimal spam thresholds to (for example) the finance and sales departments, you might better protect the finance department from spam, but you might also block some genuine sales leads due to the originator´s use of language or other spam-like component.

If you greylist inbound emails, doesn´t that delay the delivery of genuine emails?

It can, but usually by no more than a minute or two. If you are concerned about business critical emails being delayed due to the greylisting process, it is possible to selectively bypass this process by adding approved senders to a whitelist. Depending on how your spam filter for Outlook is set up, adding an approved sender to a whitelist should involve no more than the click of a mouse.

Are there any other features of a replacement filter for Outlook I should consider?

You might want to consider implementing a replacement filter for Outlook that scans outbound emails for spam and viruses. There have been cases in which business´s IP addresses have been blocked due to over-zealous spam filters flagging their outbound emails as spam. This not only affects the delivery of the business´ emails, but could also affect access to the corporate website and its position in SERPS.