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What is Microsoft's SmartScreen spam filter?

SmartScreen® is filtering technology Microsoft developed and applies across its email platforms to provide customers with the latest anti-spam and anti-phishing tools and innovations throughout its network. These products include Outlook.com, Exchange, Office 365, and others.

As of November 1, 2016, Microsoft stopped generating updates for SmartScreen spam filters in Exchange Server 2016 and earlier (2013, 2010, 2007), Outlook 2016 for Windows and earlier (2013, 2010, 2007) and Outlook 2011 for Mac. It is still used for basic protection, but its effectiveness will degrade over time. It was replaced by Exchange Online Protection (EOP), but Microsoft will merge some of the SmartScreen technology with EOP to leverage its spam fighting capabilities.

Microsoft SmartScreen
Outlook.com's SmartScreen technology screens email to identify legitimate or spam email. Based on Microsoft's machine-learning technology, the SmartScreen content filter learns from:

  • Known spam and phishing threats
  • User feedback
  • Outlook.com users who have opted into the junk classification program

This data is also an input to sender reputation.

How it works
When an email is sent to an Outlook.com account, SmartScreen screens the content of the message and assigns the message a spam confidence level (SCL). 

Outlook.com then applies SCL rating rules to the incoming email:

  • Messages with an SCL rating below a certain threshold are considered spam and deleted instead of sent to a user's junk folder.
  • Messages with an SCL rating higher than the threshold are delivered to the user's junk folder instead of the inbox.

 

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