How Does the Outlook Spam Filter Work & How to Bypass It

According to new data from Check Point, Microsoft was the most impersonated brand (38% of all brand phishing attacks) in Q1 of 2024. In one campaign that impersonated Microsoft, the attackers utilized a variety of false email subjects and sender identities to deceive recipients. The deceptive emails included subjects such as “Message Failure Delivery Notice,” “Outlook Info Replacement,” etc.

The emails contained a link, which if clicked, took recipients to a phishing website that resembled a typical Outlook login page. It aimed to trick targets into providing their login credentials, posing a major security risk for organizations.

Due to reasons like these, email clients, including Outlook, have advanced spam filters to separate spam emails from genuine ones. Let’s learn more about them, how they work, and how you can bypass them if they mark your genuine emails as spam.

What is Outlook spam filter?

Outlook spam filter (also known as junk email filter) is a feature that safeguards Outlook users from unsolicited spam emails. It serves as a crucial defense against spam, irrelevant content, and other cybersecurity threats.

The Outlook spam filter assesses multiple facets of incoming emails, including the sender’s trustworthiness, email structure, and content. By analyzing these components, the filter classifies emails into spam and genuine emails. You can read more about how it works below.

How does the Outlook spam filter work

Outlook spam filters work like any other spam filter of various email clients. It integrates advanced technologies and user input to establish a strong defense against spam. Two major techniques are used to filter out spam emails. Let’s take a look at them:

• Heuristic analysis and user input: This process involves scrutinizing emails for specific traits commonly linked with spam, such as particular phrases, suspicious sender details, unusual attachments, or irregular patterns. Emails exhibiting these characteristics are flagged as potential spam.
  
  Adding to heuristic analysis is user feedback. When users label an email as spam or not, the system learns from these actions. This manual tagging helps the filter adapt to individual user preferences and filter out the upcoming emails coming from the same sender.

• Bayesian filtering and machine learning techniques: This technique compares the content of incoming emails with previously categorized spam based on user input. It makes use of a specialized type of machine learning involving statistical methods. These algorithms analyze extensive datasets to detect intricate patterns, anticipate future behaviors, identify new spamming methods, comprehend subtle nuances in email content, and refine the filter's criteria for improved accuracy and defense against phishing and other threats.
  
  While the Outlook spam filter checks your incoming emails automatically, the email client also lets its users control how the emails are treated. Here are some features that Outlook offers to aid in better email management.

1. Safe senders and domains: You can add trusted email addresses and domains to this list and thus prevent their messages from being incorrectly flagged as junk.

2. Blocked senders and domains: This list ensures messages from specified senders or domains are automatically directed to the junk email folder.

3. Incoming mail handling: You get 2 options to choose from on how Outlook manages your emails. You can either choose to let Outlook identify possible junk emails and move them to the junk folder or you can decide who is allowed to send you emails individually.

These lists collectively contribute to a more personalized and efficient email management experience in Outlook, beyond simply filtering out unwanted emails.

How to pass through the Outlook spam filter

You can implement many generic and a few Outlook-specific practices in your email campaign to safeguard your emails from landing in the junk folder. Let’s learn about them.

1. Obtain consent

Obtaining consent from recipients, like offering double opt-in, is an effective method to reduce the risk of spam and increase the interest level of the recipient.

2. Do not use spam trigger words

Some words trigger spam filters and they land in the recipient’s spam folder. For example, using all caps and a lot of symbols in the subject line usually ends up as spam. So avoid using trigger words for better inboxing.

3. Get added to the contact list

Ask your recipients to add your email address to their contact list. If you are added to their contact list, outlook will treat your email as less spammy. Learn how to add emails to contacts in Outlook. Another thing you can do is ask them to add your email address to their safe senders list. According to Microsoft, emails or domains in the safe senders' list are never treated as spam, regardless of the content of the email.

4. Maintain a good sender reputation

Email sender reputation is a sender score assigned to each sender by an Internet service provider that sends emails. The higher the score, the more ISPs will land emails in the recipient's inbox. Maintain a positive email sender reputation by adhering to best practices such as limiting emails to targeted recipients, minimizing complaint rates, and managing email frequency responsibly.

5. Send relevant and engaging content

Nothing is more frustrating than receiving tons of irrelevant emails. If you keep sending irrelevant content and clutter their inbox, they’ll mark you as spam. This can also happen for various other reasons.

So make sure that you are targeting the right audience and sending them the content they are interested in and want to receive. You can even ask your users about what type of content they want to receive using preference centers, conducting surveys, etc.

You can also use AMP-powered interactive emails to make your emails more engaging by embedding survey forms, polls, and games within your emails.

6. Maintain a clean email list

Keep your email list clean by regularly removing inactive or invalid addresses and ensuring there's an effortless way for recipients to unsubscribe. You can also introduce a sunset policy to optimize the email list management process. This will increase your deliverability and your sender's reputation.

Conclusion

You can use many different strategies like asking your users to spam-proof your emails, sending good content, maintaining a good domain reputation, etc. But ultimately, what matters is your intention.

Do you want to help your users by giving them what they want? Or just spam their inbox in the hopes of getting a few sales? If you choose the former option, you’re already on the right track. So applying these strategies and keeping your users’ needs in mind will pave a solid foundation for your email marketing campaign.